[PATCH v2 00/10] sched: Flatten the pick

[PATCH v2 00/10] sched: Flatten the pick

[Peter Zijlstra]

Hi!

So cgroup scheduling has always been a pain in the arse. The problems start
with weight distribution and end with hierachical picks and it all sucks.

The problems with weight distribution are related to that infernal global
fraction:

             tg->w * grq_i->w
   ge_i->w = ----------------
             \Sum_j grq_j->w

which we've approximated reasonably well by now. However, the immediate
consequence of this fraction is that the total group weight (tg->w) gets
fragmented across all your CPUs. And at 64 CPUs that means your per-cpu cgroup
weight ends up being a nice 19 task worth. And more CPUs more tiny. Combine
with the fact that 256 CPU systems are relatively common these days, this
becomes painful.

The common 'solution' is to inflate the group weight by 'nr_cpus'; the
immediate problem with that is that when all load of a group gets concentrated
on a single CPU, the per-cpu cgroup weight becomes insanely large, easily
exceeding nice -20.

Additionally there are numerical limits on the max weight you can have before
the math starts suffering overflows. As such there is a definite limit on the
total group weight. Which has annoyed people ;-)

The first few patches add a knob /debug/sched/cgroup_mode and a few different
options on how to deal with this. My favourite is 'concur', but obviously that
is also the most expensive one :-/ It adds a tg->tasks counter which makes the
update_tg_load_avg() thing more expensive.

I have some ideas but I figured I ought to share these things before sinking
more time into it.


On to the hierarchical pick; this has been causing trouble for a very long
time. So once again an attempt at flatting it. The basic idea is to keep the
full hierarchical load tracking as-is, but keep all the runnable entities in a
single level. The immediate concequence of all this is ofcourse that we need to
constantly re-compute the effective weight of each entity as things progress.

Reweight is done on:
 - enqueue
 - pick -- or rather set_next_entity(.first=true)
 - tick

So while the {en,de}queue operations are still O(depth) due to the full
accounting mess, the pick is now a single level. Removing the intermediate
levels that obscure runnability etc.


For testing, I've done a little experiment, I dug out what is colloqually known
as a potato. A trusty old Sandybridge 12600k with a RX 580, and ran a game on
it. From GOG, I had available 'Shadows: Awakens', a fun title that normally
runs really well on this machine (provided you stick to 1080p).

To make it interesting, I added 8 (one for each logical CPU) copies of: 'nice
spin.sh'; this results in the game becoming almost unplayable, as in proper
terrible.

I used MangoHUD to record a few minutes of playtime for statistics, and then
quit the came and re-started it with a shorter slice set (base/10). This
results in the game being entirely playable -- not great, but definiltey
playable.

  Lutris / GE-Proton10-34 / Steam Runtime 3 (sniper)
  Intel Core i7-2600K
  AMD Radeon RX 580

  Shadows Awakening (GOG)

	  default slice(*)

  FPS min  3.8    20.6
      avg 48.0    57.2
      mag 87.4    80.3

  FT  min   9.4    8.4
      avg  34.5   19.5
      max 107.4   37.2

  FPS (Frames Per Second)
  FT  (FrameTime)

  [*] Command prefix: 'chrt -o --sched-runtime 280000 0'
      effectively setting 'base_slice_ns/10'

I have not compared to a kernel without flat on, just wanted to run non trivial
workloads and play with slice to make sure everything 'works'.


Can also be had:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/flat

 include/linux/cpuset.h |    6 
 include/linux/sched.h  |    1 
 kernel/cgroup/cpuset.c |   15 
 kernel/sched/core.c    |   47 --
 kernel/sched/debug.c   |  171 +++++---
 kernel/sched/fair.c    | 1038 ++++++++++++++++++++++---------------------------
 kernel/sched/pelt.c    |    6 
 kernel/sched/sched.h   |   44 --
 8 files changed, 672 insertions(+), 656 deletions(-)

---
Change since v1 ( https://patch.msgid.link/20260317095113.387450089@infradead.org ):
 - various Sashiko thingies
 - rebase atop curren -tip

[PATCH v2 01/10] sched/debug: Use char * instead of char (*)[]

[Peter Zijlstra]

Some of the fancy AI robots are getting 'upset'.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/debug.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -136,7 +136,7 @@ sched_feat_write(struct file *filp, cons
 	if (cnt > 63)
 		cnt = 63;
 
-	if (copy_from_user(&buf, ubuf, cnt))
+	if (copy_from_user(buf, ubuf, cnt))
 		return -EFAULT;
 
 	buf[cnt] = 0;
@@ -221,7 +221,7 @@ static ssize_t sched_dynamic_write(struc
 	if (cnt > 15)
 		cnt = 15;
 
-	if (copy_from_user(&buf, ubuf, cnt))
+	if (copy_from_user(buf, ubuf, cnt))
 		return -EFAULT;
 
 	buf[cnt] = 0;

[PATCH v2 02/10] sched: Use {READ,WRITE}_ONCE() for preempt_dynamic_mode

[Peter Zijlstra]

Robots figured out you can read and write this concurrently and got
'upset'. Gemini even noted sched_dynamic_show() can generate
'confusing' output if it observed different values during the
printing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c  |   15 ++++++++-------
 kernel/sched/debug.c |    5 +++--
 2 files changed, 11 insertions(+), 9 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7743,7 +7743,7 @@ static void __sched_dynamic_update(int m
 		break;
 	}
 
-	preempt_dynamic_mode = mode;
+	WRITE_ONCE(preempt_dynamic_mode, mode);
 }
 
 void sched_dynamic_update(int mode)
@@ -7784,12 +7784,13 @@ static void __init preempt_dynamic_init(
 	}
 }
 
-# define PREEMPT_MODEL_ACCESSOR(mode) \
-	bool preempt_model_##mode(void)						 \
-	{									 \
-		WARN_ON_ONCE(preempt_dynamic_mode == preempt_dynamic_undefined); \
-		return preempt_dynamic_mode == preempt_dynamic_##mode;		 \
-	}									 \
+# define PREEMPT_MODEL_ACCESSOR(mode)					\
+	bool preempt_model_##mode(void)					\
+	{								\
+		int mode = READ_ONCE(preempt_dynamic_mode);		\
+		WARN_ON_ONCE(mode == preempt_dynamic_undefined);	\
+		return mode == preempt_dynamic_##mode;			\
+	}								\
 	EXPORT_SYMBOL_GPL(preempt_model_##mode)
 
 PREEMPT_MODEL_ACCESSOR(none);
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -239,6 +239,7 @@ static ssize_t sched_dynamic_write(struc
 static int sched_dynamic_show(struct seq_file *m, void *v)
 {
 	int i = (IS_ENABLED(CONFIG_PREEMPT_RT) || IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY)) * 2;
+	int mode = READ_ONCE(preempt_dynamic_mode);
 	int j;
 
 	/* Count entries in NULL terminated preempt_modes */
@@ -247,10 +248,10 @@ static int sched_dynamic_show(struct seq
 	j -= !IS_ENABLED(CONFIG_ARCH_HAS_PREEMPT_LAZY);
 
 	for (; i < j; i++) {
-		if (preempt_dynamic_mode == i)
+		if (mode == i)
 			seq_puts(m, "(");
 		seq_puts(m, preempt_modes[i]);
-		if (preempt_dynamic_mode == i)
+		if (mode == i)
 			seq_puts(m, ")");
 
 		seq_puts(m, " ");

[PATCH v2 03/10] sched/debug: Collapse subsequent CONFIG_SCHED_CLASS_EXT sections

[Peter Zijlstra]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/debug.c |   92 ++++++++++++++++++++++++---------------------------
 1 file changed, 44 insertions(+), 48 deletions(-)

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -446,6 +446,8 @@ static const struct file_operations fair
 	.release	= single_release,
 };
 
+static struct dentry *debugfs_sched;
+
 #ifdef CONFIG_SCHED_CLASS_EXT
 static ssize_t
 sched_ext_server_runtime_write(struct file *filp, const char __user *ubuf,
@@ -478,75 +480,92 @@ static const struct file_operations ext_
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
-#endif /* CONFIG_SCHED_CLASS_EXT */
 
 static ssize_t
-sched_fair_server_period_write(struct file *filp, const char __user *ubuf,
-			       size_t cnt, loff_t *ppos)
+sched_ext_server_period_write(struct file *filp, const char __user *ubuf,
+			      size_t cnt, loff_t *ppos)
 {
 	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
 	struct rq *rq = cpu_rq(cpu);
 
 	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_PERIOD,
-					&rq->fair_server);
+					&rq->ext_server);
 }
 
-static int sched_fair_server_period_show(struct seq_file *m, void *v)
+static int sched_ext_server_period_show(struct seq_file *m, void *v)
 {
 	unsigned long cpu = (unsigned long) m->private;
 	struct rq *rq = cpu_rq(cpu);
 
-	return sched_server_show_common(m, v, DL_PERIOD, &rq->fair_server);
+	return sched_server_show_common(m, v, DL_PERIOD, &rq->ext_server);
 }
 
-static int sched_fair_server_period_open(struct inode *inode, struct file *filp)
+static int sched_ext_server_period_open(struct inode *inode, struct file *filp)
 {
-	return single_open(filp, sched_fair_server_period_show, inode->i_private);
+	return single_open(filp, sched_ext_server_period_show, inode->i_private);
 }
 
-static const struct file_operations fair_server_period_fops = {
-	.open		= sched_fair_server_period_open,
-	.write		= sched_fair_server_period_write,
+static const struct file_operations ext_server_period_fops = {
+	.open		= sched_ext_server_period_open,
+	.write		= sched_ext_server_period_write,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
 
-#ifdef CONFIG_SCHED_CLASS_EXT
+static void debugfs_ext_server_init(void)
+{
+	struct dentry *d_ext;
+	unsigned long cpu;
+
+	d_ext = debugfs_create_dir("ext_server", debugfs_sched);
+	if (!d_ext)
+		return;
+
+	for_each_possible_cpu(cpu) {
+		struct dentry *d_cpu;
+		char buf[32];
+
+		snprintf(buf, sizeof(buf), "cpu%lu", cpu);
+		d_cpu = debugfs_create_dir(buf, d_ext);
+
+		debugfs_create_file("runtime", 0644, d_cpu, (void *) cpu, &ext_server_runtime_fops);
+		debugfs_create_file("period", 0644, d_cpu, (void *) cpu, &ext_server_period_fops);
+	}
+}
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
 static ssize_t
-sched_ext_server_period_write(struct file *filp, const char __user *ubuf,
-			      size_t cnt, loff_t *ppos)
+sched_fair_server_period_write(struct file *filp, const char __user *ubuf,
+			       size_t cnt, loff_t *ppos)
 {
 	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
 	struct rq *rq = cpu_rq(cpu);
 
 	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_PERIOD,
-					&rq->ext_server);
+					&rq->fair_server);
 }
 
-static int sched_ext_server_period_show(struct seq_file *m, void *v)
+static int sched_fair_server_period_show(struct seq_file *m, void *v)
 {
 	unsigned long cpu = (unsigned long) m->private;
 	struct rq *rq = cpu_rq(cpu);
 
-	return sched_server_show_common(m, v, DL_PERIOD, &rq->ext_server);
+	return sched_server_show_common(m, v, DL_PERIOD, &rq->fair_server);
 }
 
-static int sched_ext_server_period_open(struct inode *inode, struct file *filp)
+static int sched_fair_server_period_open(struct inode *inode, struct file *filp)
 {
-	return single_open(filp, sched_ext_server_period_show, inode->i_private);
+	return single_open(filp, sched_fair_server_period_show, inode->i_private);
 }
 
-static const struct file_operations ext_server_period_fops = {
-	.open		= sched_ext_server_period_open,
-	.write		= sched_ext_server_period_write,
+static const struct file_operations fair_server_period_fops = {
+	.open		= sched_fair_server_period_open,
+	.write		= sched_fair_server_period_write,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
-#endif /* CONFIG_SCHED_CLASS_EXT */
-
-static struct dentry *debugfs_sched;
 
 static void debugfs_fair_server_init(void)
 {
@@ -569,29 +588,6 @@ static void debugfs_fair_server_init(voi
 	}
 }
 
-#ifdef CONFIG_SCHED_CLASS_EXT
-static void debugfs_ext_server_init(void)
-{
-	struct dentry *d_ext;
-	unsigned long cpu;
-
-	d_ext = debugfs_create_dir("ext_server", debugfs_sched);
-	if (!d_ext)
-		return;
-
-	for_each_possible_cpu(cpu) {
-		struct dentry *d_cpu;
-		char buf[32];
-
-		snprintf(buf, sizeof(buf), "cpu%lu", cpu);
-		d_cpu = debugfs_create_dir(buf, d_ext);
-
-		debugfs_create_file("runtime", 0644, d_cpu, (void *) cpu, &ext_server_runtime_fops);
-		debugfs_create_file("period", 0644, d_cpu, (void *) cpu, &ext_server_period_fops);
-	}
-}
-#endif /* CONFIG_SCHED_CLASS_EXT */
-
 static __init int sched_init_debug(void)
 {
 	struct dentry __maybe_unused *numa;

[PATCH v2 04/10] sched/fair: Add cgroup_mode switch

[Peter Zijlstra]

Since calc_group_shares() has issues with 'many' CPUs, specifically the
computed shares value gets to be roughly 1/nr_cpus, prepare to add a few
alternative methods.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/debug.c |   74 +++++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/sched/sched.h |    1 
 2 files changed, 75 insertions(+)

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -588,6 +588,76 @@ static void debugfs_fair_server_init(voi
 	}
 }
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+int cgroup_mode = 0;
+
+static const char *cgroup_mode_str[] = {
+	"smp",
+};
+
+static int sched_cgroup_mode(const char *str)
+{
+	for (int i = 0; i < ARRAY_SIZE(cgroup_mode_str); i++) {
+		if (!strcmp(str, cgroup_mode_str[i]))
+			return i;
+	}
+	return -EINVAL;
+}
+
+static ssize_t sched_cgroup_write(struct file *filp, const char __user *ubuf,
+				   size_t cnt, loff_t *ppos)
+{
+	char buf[16];
+	int mode;
+
+	if (cnt > 15)
+		cnt = 15;
+
+	if (copy_from_user(buf, ubuf, cnt))
+		return -EFAULT;
+
+	buf[cnt] = 0;
+	mode = sched_cgroup_mode(strstrip(buf));
+	if (mode < 0)
+		return mode;
+
+	WRITE_ONCE(cgroup_mode, mode);
+
+	*ppos += cnt;
+	return cnt;
+}
+
+static int sched_cgroup_show(struct seq_file *m, void *v)
+{
+	int mode = READ_ONCE(cgroup_mode);
+
+	for (int i = 0; i < ARRAY_SIZE(cgroup_mode_str); i++) {
+		if (mode == i)
+			seq_puts(m, "(");
+		seq_puts(m, cgroup_mode_str[i]);
+		if (mode == i)
+			seq_puts(m, ")");
+
+		seq_puts(m, " ");
+	}
+	seq_puts(m, "\n");
+	return 0;
+}
+
+static int sched_cgroup_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_cgroup_show, NULL);
+}
+
+static const struct file_operations sched_cgroup_fops = {
+	.open		= sched_cgroup_open,
+	.write		= sched_cgroup_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+#endif
+
 static __init int sched_init_debug(void)
 {
 	struct dentry __maybe_unused *numa;
@@ -625,6 +695,10 @@ static __init int sched_init_debug(void)
 
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+	debugfs_create_file("cgroup_mode", 0644, debugfs_sched, NULL, &sched_cgroup_fops);
+#endif
+
 	debugfs_fair_server_init();
 #ifdef CONFIG_SCHED_CLASS_EXT
 	debugfs_ext_server_init();
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -565,6 +565,7 @@ static inline struct task_group *css_tg(
 extern int tg_nop(struct task_group *tg, void *data);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
+extern int cgroup_mode;
 extern void free_fair_sched_group(struct task_group *tg);
 extern int alloc_fair_sched_group(struct task_group *tg, struct task_group *parent);
 extern void online_fair_sched_group(struct task_group *tg);

[PATCH v2 05/10] sched/fair: Add cgroup_mode: UP

[Peter Zijlstra]

Instead of calculating the proportional fraction of tg->shares for
each CPU, just give each CPU the full measure, ignoring these pesky
SMP problems.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/debug.c |    3 ++-
 kernel/sched/fair.c  |   21 ++++++++++++++++++++-
 2 files changed, 22 insertions(+), 2 deletions(-)

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -589,9 +589,10 @@ static void debugfs_fair_server_init(voi
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
-int cgroup_mode = 0;
+int cgroup_mode = 1;
 
 static const char *cgroup_mode_str[] = {
+	"up",
 	"smp",
 };
 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4150,7 +4150,7 @@ static inline int throttled_hierarchy(st
  *
  * hence icky!
  */
-static long calc_group_shares(struct cfs_rq *cfs_rq)
+static long calc_smp_shares(struct cfs_rq *cfs_rq)
 {
 	long tg_weight, tg_shares, load, shares;
 	struct task_group *tg = cfs_rq->tg;
@@ -4185,6 +4185,25 @@ static long calc_group_shares(struct cfs
 }
 
 /*
+ * Ignore this pesky SMP stuff, use (4).
+ */
+static long calc_up_shares(struct cfs_rq *cfs_rq)
+{
+	struct task_group *tg = cfs_rq->tg;
+	return READ_ONCE(tg->shares);
+}
+
+static long calc_group_shares(struct cfs_rq *cfs_rq)
+{
+	int mode = READ_ONCE(cgroup_mode);
+
+	if (mode == 0)
+		return calc_up_shares(cfs_rq);
+
+	return calc_smp_shares(cfs_rq);
+}
+
+/*
  * Recomputes the group entity based on the current state of its group
  * runqueue.
  */

[PATCH v2 06/10] sched/fair: Add cgroup_mode: MAX

[Peter Zijlstra]

In order to avoid the CPU shares becoming tiny '1 / nr_cpus', assume each
cgroup is maximally concurrent and distrubute 'nr_cpus * tg->shares',
such that each CPU ends up with a 'tg->shares' sized fraction (on
average).

There is the corner case, when a cgroup is minimally loaded, eg a
single spinner, therefore limit the CPU shares to that of a nice -20
task to avoid getting too much load.

It was previously suggested to allow raising cpu.weight to '100 * nr_cpus'
to combat this same problem, but the problem there is the above corner case,
allowing multiple cgroups with such immense weight to the runqueue has
significant problems.

It would drown the kthreads, but it also risks overflowing the load values.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/cpuset.h |    6 +++++
 kernel/cgroup/cpuset.c |   15 ++++++++++++++
 kernel/sched/debug.c   |    1 
 kernel/sched/fair.c    |   52 ++++++++++++++++++++++++++++++++++++++++++++-----
 4 files changed, 69 insertions(+), 5 deletions(-)

--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -80,6 +80,7 @@ extern void lockdep_assert_cpuset_lock_h
 extern void cpuset_cpus_allowed_locked(struct task_struct *p, struct cpumask *mask);
 extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
 extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern int cpuset_num_cpus(struct cgroup *cgroup);
 extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
 #define cpuset_current_mems_allowed (current->mems_allowed)
 void cpuset_init_current_mems_allowed(void);
@@ -216,6 +217,11 @@ static inline bool cpuset_cpus_allowed_f
 	return false;
 }
 
+static inline int cpuset_num_cpus(struct cgroup *cgroup)
+{
+	return num_online_cpus();
+}
+
 static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
 {
 	return node_possible_map;
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -4100,6 +4100,21 @@ bool cpuset_cpus_allowed_fallback(struct
 	return changed;
 }
 
+int cpuset_num_cpus(struct cgroup *cgrp)
+{
+	int nr = num_online_cpus();
+	struct cpuset *cs;
+
+	if (is_in_v2_mode()) {
+		guard(rcu)();
+		cs = css_cs(cgroup_e_css(cgrp, &cpuset_cgrp_subsys));
+		if (cs)
+			nr = cpumask_weight(cs->effective_cpus);
+	}
+
+	return nr;
+}
+
 void __init cpuset_init_current_mems_allowed(void)
 {
 	nodes_setall(current->mems_allowed);
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -594,6 +594,7 @@ int cgroup_mode = 1;
 static const char *cgroup_mode_str[] = {
 	"up",
 	"smp",
+	"max",
 };
 
 static int sched_cgroup_mode(const char *str)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4150,12 +4150,10 @@ static inline int throttled_hierarchy(st
  *
  * hence icky!
  */
-static long calc_smp_shares(struct cfs_rq *cfs_rq)
+static long __calc_smp_shares(struct cfs_rq *cfs_rq, long tg_shares, long shares_max)
 {
-	long tg_weight, tg_shares, load, shares;
 	struct task_group *tg = cfs_rq->tg;
-
-	tg_shares = READ_ONCE(tg->shares);
+	long tg_weight, load, shares;
 
 	load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg);
 
@@ -4181,7 +4179,48 @@ static long calc_smp_shares(struct cfs_r
 	 * case no task is runnable on a CPU MIN_SHARES=2 should be returned
 	 * instead of 0.
 	 */
-	return clamp_t(long, shares, MIN_SHARES, tg_shares);
+	return clamp_t(long, shares, MIN_SHARES, shares_max);
+}
+
+static int tg_cpus(struct task_group *tg)
+{
+	int nr = num_online_cpus();
+
+	if (cpusets_enabled()) {
+		struct cgroup *cgrp = tg->css.cgroup;
+		if (cgrp)
+			nr = cpuset_num_cpus(cgrp);
+	}
+
+	return nr;
+}
+
+/*
+ * Func: min(fraction(num_cpus * tg->shares), nice -20)
+ *
+ * Scale tg->shares by the maximal number of CPUs; but clip the max shares at
+ * nice -20, otherwise a single spinner on a 512 CPU machine would result in
+ * 512*NICE_0_LOAD, which is also crazy.
+ */
+static long calc_max_shares(struct cfs_rq *cfs_rq)
+{
+	struct task_group *tg = cfs_rq->tg;
+	int nr = tg_cpus(tg);
+	long tg_shares = READ_ONCE(tg->shares);
+	long max_shares = scale_load(sched_prio_to_weight[0]);
+	return __calc_smp_shares(cfs_rq, tg_shares * nr, max_shares);
+}
+
+/*
+ * Func: fraction(tg->shares)
+ *
+ * This infamously results in tiny shares when you have many CPUs.
+ */
+static long calc_smp_shares(struct cfs_rq *cfs_rq)
+{
+	struct task_group *tg = cfs_rq->tg;
+	long tg_shares = READ_ONCE(tg->shares);
+	return __calc_smp_shares(cfs_rq, tg_shares, tg_shares);
 }
 
 /*
@@ -4200,6 +4239,9 @@ static long calc_group_shares(struct cfs
 	if (mode == 0)
 		return calc_up_shares(cfs_rq);
 
+	if (mode == 2)
+		return calc_max_shares(cfs_rq);
+
 	return calc_smp_shares(cfs_rq);
 }
 

[PATCH v2 07/10] sched/fair: Add cgroup_mode: CONCUR

[Peter Zijlstra]

A variation of MAX; where instead of assuming maximal concurrent, this scales
with 'min(nr_tasks, nr_cpus)'. This handles the low concurrency cases more
gracefully, with the exception of CPU affnity.

Note: the tracking of tg->tasks is somewhat expensive :-/

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/debug.c |    1 +
 kernel/sched/fair.c  |   39 ++++++++++++++++++++++++++++++++++++---
 kernel/sched/sched.h |    3 +++
 3 files changed, 40 insertions(+), 3 deletions(-)

--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -594,6 +594,7 @@ int cgroup_mode = 1;
 static const char *cgroup_mode_str[] = {
 	"up",
 	"smp",
+	"concur",
 	"max",
 };
 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4211,6 +4211,30 @@ static long calc_max_shares(struct cfs_r
 	return __calc_smp_shares(cfs_rq, tg_shares * nr, max_shares);
 }
 
+static inline int tg_tasks(struct task_group *tg)
+{
+	return max(1, atomic_long_read(&tg->tasks));
+}
+
+/*
+ * Func: min(fraction(num * tg->shares), nice -20); where
+ *       num = min(nr_tasks, nr_cpus)
+ *
+ * Similar to max, except scale with min(nr_tasks, nr_cpus), which gives
+ * a far more natural distrubution. Can still create edge case using CPU
+ * affinity.
+ */
+static long calc_concur_shares(struct cfs_rq *cfs_rq)
+{
+	struct task_group *tg = cfs_rq->tg;
+	int nr_cpus = tg_cpus(tg);
+	int nr_tasks = tg_tasks(tg);
+	int nr = min(nr_tasks, nr_cpus);
+	long tg_shares = READ_ONCE(tg->shares);
+	long max_shares = scale_load(sched_prio_to_weight[0]);
+	return __calc_smp_shares(cfs_rq, nr * tg_shares, max_shares);
+}
+
 /*
  * Func: fraction(tg->shares)
  *
@@ -4240,6 +4264,9 @@ static long calc_group_shares(struct cfs
 		return calc_up_shares(cfs_rq);
 
 	if (mode == 2)
+		return calc_concur_shares(cfs_rq);
+
+	if (mode == 3)
 		return calc_max_shares(cfs_rq);
 
 	return calc_smp_shares(cfs_rq);
@@ -4385,7 +4412,7 @@ static inline bool cfs_rq_is_decayed(str
  */
 static inline void update_tg_load_avg(struct cfs_rq *cfs_rq)
 {
-	long delta;
+	long delta, dt;
 	u64 now;
 
 	/*
@@ -4407,16 +4434,19 @@ static inline void update_tg_load_avg(st
 		return;
 
 	delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;
-	if (abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
+	dt = cfs_rq->h_nr_queued - cfs_rq->tg_tasks_contrib;
+	if (dt || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
 		atomic_long_add(delta, &cfs_rq->tg->load_avg);
+		atomic_long_add(dt, &cfs_rq->tg->tasks);
 		cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
+		cfs_rq->tg_tasks_contrib = cfs_rq->h_nr_queued;
 		cfs_rq->last_update_tg_load_avg = now;
 	}
 }
 
 static inline void clear_tg_load_avg(struct cfs_rq *cfs_rq)
 {
-	long delta;
+	long delta, dt;
 	u64 now;
 
 	/*
@@ -4427,8 +4457,11 @@ static inline void clear_tg_load_avg(str
 
 	now = sched_clock_cpu(cpu_of(rq_of(cfs_rq)));
 	delta = 0 - cfs_rq->tg_load_avg_contrib;
+	dt = 0 - cfs_rq->tg_tasks_contrib;
 	atomic_long_add(delta, &cfs_rq->tg->load_avg);
+	atomic_long_add(dt, &cfs_rq->tg->tasks);
 	cfs_rq->tg_load_avg_contrib = 0;
+	cfs_rq->tg_tasks_contrib = 0;
 	cfs_rq->last_update_tg_load_avg = now;
 }
 
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -491,6 +491,8 @@ struct task_group {
 	 * will also be accessed at each tick.
 	 */
 	atomic_long_t		load_avg ____cacheline_aligned;
+	atomic_long_t		tasks;
+
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #ifdef CONFIG_RT_GROUP_SCHED
@@ -720,6 +722,7 @@ struct cfs_rq {
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	u64			last_update_tg_load_avg;
 	unsigned long		tg_load_avg_contrib;
+	unsigned long		tg_tasks_contrib;
 	long			propagate;
 	long			prop_runnable_sum;
 

[PATCH v2 08/10] sched/fair: Add newidle balance to pick_task_fair()

[Peter Zijlstra]

With commit 50653216e4ff ("sched: Add support to pick functions to
take rf") removing the balance callback, the pick_task() callback is
in charge of newidle balancing.

This means pick_task_fair() should do so too. This hasn't been a
problem in practise because pick_next_task_fair() is used. However,
since we'll be removing that one shortly, make sure pick_next_task()
is up to scratch.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/fair.c |   38 +++++++++++++++-----------------------
 1 file changed, 15 insertions(+), 23 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9215,16 +9215,18 @@ static void wakeup_preempt_fair(struct r
 }
 
 static struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
+	__must_hold(__rq_lockp(rq))
 {
 	struct sched_entity *se;
 	struct cfs_rq *cfs_rq;
 	struct task_struct *p;
 	bool throttled;
+	int new_tasks;
 
 again:
 	cfs_rq = &rq->cfs;
 	if (!cfs_rq->nr_queued)
-		return NULL;
+		goto idle;
 
 	throttled = false;
 
@@ -9245,6 +9247,14 @@ static struct task_struct *pick_task_fai
 	if (unlikely(throttled))
 		task_throttle_setup_work(p);
 	return p;
+
+idle:
+	new_tasks = sched_balance_newidle(rq, rf);
+	if (new_tasks < 0)
+		return RETRY_TASK;
+	if (new_tasks > 0)
+		goto again;
+	return NULL;
 }
 
 static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first);
@@ -9256,12 +9266,12 @@ pick_next_task_fair(struct rq *rq, struc
 {
 	struct sched_entity *se;
 	struct task_struct *p;
-	int new_tasks;
 
-again:
 	p = pick_task_fair(rq, rf);
+	if (unlikely(p == RETRY_TASK))
+		return p;
 	if (!p)
-		goto idle;
+		return p;
 	se = &p->se;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -9311,29 +9321,11 @@ pick_next_task_fair(struct rq *rq, struc
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 	put_prev_set_next_task(rq, prev, p);
 	return p;
-
-idle:
-	if (rf) {
-		new_tasks = sched_balance_newidle(rq, rf);
-
-		/*
-		 * Because sched_balance_newidle() releases (and re-acquires)
-		 * rq->lock, it is possible for any higher priority task to
-		 * appear. In that case we must re-start the pick_next_entity()
-		 * loop.
-		 */
-		if (new_tasks < 0)
-			return RETRY_TASK;
-
-		if (new_tasks > 0)
-			goto again;
-	}
-
-	return NULL;
 }
 
 static struct task_struct *
 fair_server_pick_task(struct sched_dl_entity *dl_se, struct rq_flags *rf)
+	__must_hold(__rq_lockp(dl_se->rq))
 {
 	return pick_task_fair(dl_se->rq, rf);
 }

Re: [PATCH v2 08/10] sched/fair: Add newidle balance to pick_task_fair()

[K Prateek Nayak]

Hello Peter,

On 5/11/2026 5:01 PM, Peter Zijlstra wrote:
> @@ -9245,6 +9247,14 @@ static struct task_struct *pick_task_fai
>  	if (unlikely(throttled))
>  		task_throttle_setup_work(p);
>  	return p;
> +
> +idle:
> +	new_tasks = sched_balance_newidle(rq, rf);
> +	if (new_tasks < 0)
> +		return RETRY_TASK;
> +	if (new_tasks > 0)
> +		goto again;
> +	return NULL;
>  }

For core scheduling will now trigger a newidle balance during the pick
when core_cookie is reset to 0 which can cause tasks to migrate only
for them to find they cannot run on the CPU since core-wide selection
leads to a cookie mismatch and it is kept hanging there.

Can we return early if sched_core_enabled() here or are the additional
newidle balance okay?

-- 
Thanks and Regards,
Prateek

Re: [PATCH v2 08/10] sched/fair: Add newidle balance to pick_task_fair()

[Peter Zijlstra]

On Tue, May 12, 2026 at 11:07:13AM +0530, K Prateek Nayak wrote:
> Hello Peter,
> 
> On 5/11/2026 5:01 PM, Peter Zijlstra wrote:
> > @@ -9245,6 +9247,14 @@ static struct task_struct *pick_task_fai
> >  	if (unlikely(throttled))
> >  		task_throttle_setup_work(p);
> >  	return p;
> > +
> > +idle:
> > +	new_tasks = sched_balance_newidle(rq, rf);
> > +	if (new_tasks < 0)
> > +		return RETRY_TASK;
> > +	if (new_tasks > 0)
> > +		goto again;
> > +	return NULL;
> >  }
> 
> For core scheduling will now trigger a newidle balance during the pick
> when core_cookie is reset to 0 which can cause tasks to migrate only
> for them to find they cannot run on the CPU since core-wide selection
> leads to a cookie mismatch and it is kept hanging there.
> 
> Can we return early if sched_core_enabled() here or are the additional
> newidle balance okay?

This basically makes fair behave like every other class, so in that sense
this is probably okay. That said, fair is the most common case, so
perhaps.

Lets see if the people actually using this notice first though ;-)

[PATCH v2 09/10] sched: Remove sched_class::pick_next_task()

[Peter Zijlstra]

The reason for pick_next_task_fair() is the put/set optimization that
avoids touching the common ancestors. However, it is possible to
implement this in the put_prev_task() and set_next_task() calls as
used in put_prev_set_next_task().

Notably, put_prev_set_next_task() is the only site that:

 - calls put_prev_task() with a .next argument;
 - calls set_next_task() with .first = true.

This means that put_prev_task() can determine the common hierarchy and
stop there, and then set_next_task() can terminate where put_prev_task
stopped.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c  |   27 +++------
 kernel/sched/fair.c  |  139 +++++++++++++++++----------------------------------
 kernel/sched/sched.h |   14 -----
 3 files changed, 57 insertions(+), 123 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5980,16 +5980,15 @@ __pick_next_task(struct rq *rq, struct t
 	if (likely(!sched_class_above(prev->sched_class, &fair_sched_class) &&
 		   rq->nr_running == rq->cfs.h_nr_queued)) {
 
-		p = pick_next_task_fair(rq, prev, rf);
+		p = pick_task_fair(rq, rf);
 		if (unlikely(p == RETRY_TASK))
 			goto restart;
 
 		/* Assume the next prioritized class is idle_sched_class */
-		if (!p) {
+		if (!p)
 			p = pick_task_idle(rq, rf);
-			put_prev_set_next_task(rq, prev, p);
-		}
 
+		put_prev_set_next_task(rq, prev, p);
 		return p;
 	}
 
@@ -5997,20 +5996,12 @@ __pick_next_task(struct rq *rq, struct t
 	prev_balance(rq, prev, rf);
 
 	for_each_active_class(class) {
-		if (class->pick_next_task) {
-			p = class->pick_next_task(rq, prev, rf);
-			if (unlikely(p == RETRY_TASK))
-				goto restart;
-			if (p)
-				return p;
-		} else {
-			p = class->pick_task(rq, rf);
-			if (unlikely(p == RETRY_TASK))
-				goto restart;
-			if (p) {
-				put_prev_set_next_task(rq, prev, p);
-				return p;
-			}
+		p = class->pick_task(rq, rf);
+		if (unlikely(p == RETRY_TASK))
+			goto restart;
+		if (p) {
+			put_prev_set_next_task(rq, prev, p);
+			return p;
 		}
 	}
 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9214,7 +9214,7 @@ static void wakeup_preempt_fair(struct r
 	resched_curr_lazy(rq);
 }
 
-static struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
+struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
 	__must_hold(__rq_lockp(rq))
 {
 	struct sched_entity *se;
@@ -9257,72 +9257,6 @@ static struct task_struct *pick_task_fai
 	return NULL;
 }
 
-static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first);
-static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first);
-
-struct task_struct *
-pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
-	__must_hold(__rq_lockp(rq))
-{
-	struct sched_entity *se;
-	struct task_struct *p;
-
-	p = pick_task_fair(rq, rf);
-	if (unlikely(p == RETRY_TASK))
-		return p;
-	if (!p)
-		return p;
-	se = &p->se;
-
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	if (prev->sched_class != &fair_sched_class)
-		goto simple;
-
-	__put_prev_set_next_dl_server(rq, prev, p);
-
-	/*
-	 * Because of the set_next_buddy() in dequeue_task_fair() it is rather
-	 * likely that a next task is from the same cgroup as the current.
-	 *
-	 * Therefore attempt to avoid putting and setting the entire cgroup
-	 * hierarchy, only change the part that actually changes.
-	 *
-	 * Since we haven't yet done put_prev_entity and if the selected task
-	 * is a different task than we started out with, try and touch the
-	 * least amount of cfs_rqs.
-	 */
-	if (prev != p) {
-		struct sched_entity *pse = &prev->se;
-		struct cfs_rq *cfs_rq;
-
-		while (!(cfs_rq = is_same_group(se, pse))) {
-			int se_depth = se->depth;
-			int pse_depth = pse->depth;
-
-			if (se_depth <= pse_depth) {
-				put_prev_entity(cfs_rq_of(pse), pse);
-				pse = parent_entity(pse);
-			}
-			if (se_depth >= pse_depth) {
-				set_next_entity(cfs_rq_of(se), se, true);
-				se = parent_entity(se);
-			}
-		}
-
-		put_prev_entity(cfs_rq, pse);
-		set_next_entity(cfs_rq, se, true);
-
-		__set_next_task_fair(rq, p, true);
-	}
-
-	return p;
-
-simple:
-#endif /* CONFIG_FAIR_GROUP_SCHED */
-	put_prev_set_next_task(rq, prev, p);
-	return p;
-}
-
 static struct task_struct *
 fair_server_pick_task(struct sched_dl_entity *dl_se, struct rq_flags *rf)
 	__must_hold(__rq_lockp(dl_se->rq))
@@ -9346,10 +9280,33 @@ static void put_prev_task_fair(struct rq
 {
 	struct sched_entity *se = &prev->se;
 	struct cfs_rq *cfs_rq;
+	struct sched_entity *nse = NULL;
 
-	for_each_sched_entity(se) {
+#ifdef CONFIG_FAIR_GROUP_SCHED
+	if (next && next->sched_class == &fair_sched_class)
+		nse = &next->se;
+#endif
+
+	while (se) {
 		cfs_rq = cfs_rq_of(se);
-		put_prev_entity(cfs_rq, se);
+		if (!nse || cfs_rq->curr)
+			put_prev_entity(cfs_rq, se);
+#ifdef CONFIG_FAIR_GROUP_SCHED
+		if (nse) {
+			if (is_same_group(se, nse))
+				break;
+
+			int d = nse->depth - se->depth;
+			if (d >= 0) {
+				/* nse has equal or greater depth, ascend */
+				nse = parent_entity(nse);
+				/* if nse is the deeper, do not ascend se */
+				if (d > 0)
+					continue;
+			}
+		}
+#endif
+		se = parent_entity(se);
 	}
 }
 
@@ -13896,10 +13853,30 @@ static void switched_to_fair(struct rq *
 	}
 }
 
-static void __set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
+/*
+ * Account for a task changing its policy or group.
+ *
+ * This routine is mostly called to set cfs_rq->curr field when a task
+ * migrates between groups/classes.
+ */
+static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 {
 	struct sched_entity *se = &p->se;
 
+	for_each_sched_entity(se) {
+		struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+		if (IS_ENABLED(CONFIG_FAIR_GROUP_SCHED) &&
+		    first && cfs_rq->curr)
+			break;
+
+		set_next_entity(cfs_rq, se, first);
+		/* ensure bandwidth has been allocated on our new cfs_rq */
+		account_cfs_rq_runtime(cfs_rq, 0);
+	}
+
+	se = &p->se;
+
 	if (task_on_rq_queued(p)) {
 		/*
 		 * Move the next running task to the front of the list, so our
@@ -13919,27 +13896,6 @@ static void __set_next_task_fair(struct
 	sched_fair_update_stop_tick(rq, p);
 }
 
-/*
- * Account for a task changing its policy or group.
- *
- * This routine is mostly called to set cfs_rq->curr field when a task
- * migrates between groups/classes.
- */
-static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
-{
-	struct sched_entity *se = &p->se;
-
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-
-		set_next_entity(cfs_rq, se, first);
-		/* ensure bandwidth has been allocated on our new cfs_rq */
-		account_cfs_rq_runtime(cfs_rq, 0);
-	}
-
-	__set_next_task_fair(rq, p, first);
-}
-
 void init_cfs_rq(struct cfs_rq *cfs_rq)
 {
 	cfs_rq->tasks_timeline = RB_ROOT_CACHED;
@@ -14251,7 +14207,6 @@ DEFINE_SCHED_CLASS(fair) = {
 	.wakeup_preempt		= wakeup_preempt_fair,
 
 	.pick_task		= pick_task_fair,
-	.pick_next_task		= pick_next_task_fair,
 	.put_prev_task		= put_prev_task_fair,
 	.set_next_task          = set_next_task_fair,
 
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2555,17 +2555,6 @@ struct sched_class {
 	 * schedule/pick_next_task: rq->lock
 	 */
 	struct task_struct *(*pick_task)(struct rq *rq, struct rq_flags *rf);
-	/*
-	 * Optional! When implemented pick_next_task() should be equivalent to:
-	 *
-	 *   next = pick_task();
-	 *   if (next) {
-	 *       put_prev_task(prev);
-	 *       set_next_task_first(next);
-	 *   }
-	 */
-	struct task_struct *(*pick_next_task)(struct rq *rq, struct task_struct *prev,
-					      struct rq_flags *rf);
 
 	/*
 	 * sched_change:
@@ -2789,8 +2778,7 @@ static inline bool sched_fair_runnable(s
 	return rq->cfs.nr_queued > 0;
 }
 
-extern struct task_struct *pick_next_task_fair(struct rq *rq, struct task_struct *prev,
-					       struct rq_flags *rf);
+extern struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf);
 extern struct task_struct *pick_task_idle(struct rq *rq, struct rq_flags *rf);
 
 #define SCA_CHECK		0x01

[PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[Peter Zijlstra]

Change fair/cgroup to a single runqueue.

Infamously fair/cgroup isn't working for a number of people; typically
the complaint is latencies and/or overhead. The latency issue is due
to the intermediate entries that represent a combination of tasks and
thereby obfuscate the runnability of tasks.

The approach here is to leave the cgroup hierarchy as is; including
the intermediate enqueue/dequeue but move the actual EEVDF runqueue
outside. This means things like the shares_weight approximation are
fully preserved.

That is, given a hierarchy like:

        R
        |
        se--G1
            / \
      G2--se   se--G3
     / \           |
T1--se se--T2      se--T3

This is fully maintained for load tracking, however the EEVDF parts of
cfs_rq/se go unused for the intermediates and are instead connected
like:

     _R_
    / | \
   T1 T2 T3

Since the effective weight of the entities is determined by the
hierarchy, this gets recomputed on enqueue,set_next_task and tick.

Notably, the effective weight (se->h_load) is computed from the
hierarchical fraction: se->load / cfs_rq->load.

Since EEVDF is now exclusive operating on rq->cfs, it needs to
consider cfs_rq->h_nr_queued rather than cfs_rq->nr_queued. Similarly,
only tasks can get delayed, simplifying some of the cgroup cleanup.

One place where additional information was required was
set_next_task() / put_prev_task(), where we need to track 'current'
both in the hierarchical sense (cfs_rq->h_curr) and in the flat sense
(cfs_rq->curr).

As a result of only having a single level to pick from, much of the
complications in pick_next_task() and preemption go away.

Since many of the hierarchical operations are still there, this won't
immediately fix the performance issues, but hopefully it will fix some
of the latency issues.

TODO: split struct cfs_rq / struct sched_entity
TODO: try and get rid of h_curr

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/sched.h |    1 
 kernel/sched/core.c   |    5 
 kernel/sched/debug.c  |    9 
 kernel/sched/fair.c   |  789 +++++++++++++++++++++-----------------------------
 kernel/sched/pelt.c   |    6 
 kernel/sched/sched.h  |   26 -
 6 files changed, 366 insertions(+), 470 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -575,6 +575,7 @@ struct sched_statistics {
 struct sched_entity {
 	/* For load-balancing: */
 	struct load_weight		load;
+	struct load_weight		h_load;
 	struct rb_node			run_node;
 	u64				deadline;
 	u64				min_vruntime;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5539,11 +5539,8 @@ EXPORT_PER_CPU_SYMBOL(kernel_cpustat);
  */
 static inline void prefetch_curr_exec_start(struct task_struct *p)
 {
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	struct sched_entity *curr = p->se.cfs_rq->curr;
-#else
 	struct sched_entity *curr = task_rq(p)->cfs.curr;
-#endif
+
 	prefetch(curr);
 	prefetch(&curr->exec_start);
 }
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -911,10 +911,11 @@ print_task(struct seq_file *m, struct rq
 	else
 		SEQ_printf(m, " %c", task_state_to_char(p));
 
-	SEQ_printf(m, " %15s %5d %9Ld.%06ld   %c   %9Ld.%06ld %c %9Ld.%06ld %9Ld.%06ld %9Ld   %5d ",
+	SEQ_printf(m, " %15s %5d %10ld %9Ld.%06ld   %c   %9Ld.%06ld %c %9Ld.%06ld %9Ld.%06ld %9Ld   %5d ",
 		p->comm, task_pid_nr(p),
+		p->se.h_load.weight,
 		SPLIT_NS(p->se.vruntime),
-		entity_eligible(cfs_rq_of(&p->se), &p->se) ? 'E' : 'N',
+		entity_eligible(&rq->cfs, &p->se) ? 'E' : 'N',
 		SPLIT_NS(p->se.deadline),
 		p->se.custom_slice ? 'S' : ' ',
 		SPLIT_NS(p->se.slice),
@@ -943,7 +944,7 @@ static void print_rq(struct seq_file *m,
 
 	SEQ_printf(m, "\n");
 	SEQ_printf(m, "runnable tasks:\n");
-	SEQ_printf(m, " S            task   PID       vruntime   eligible    "
+	SEQ_printf(m, " S            task   PID     weight       vruntime   eligible    "
 		   "deadline             slice          sum-exec      switches  "
 		   "prio         wait-time        sum-sleep       sum-block"
 #ifdef CONFIG_NUMA_BALANCING
@@ -1051,6 +1052,8 @@ void print_cfs_rq(struct seq_file *m, in
 			cfs_rq->tg_load_avg_contrib);
 	SEQ_printf(m, "  .%-30s: %ld\n", "tg_load_avg",
 			atomic_long_read(&cfs_rq->tg->load_avg));
+	SEQ_printf(m, "  .%-30s: %lu\n", "h_load",
+			cfs_rq->h_load);
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 #ifdef CONFIG_CFS_BANDWIDTH
 	SEQ_printf(m, "  .%-30s: %d\n", "throttled",
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -296,8 +296,8 @@ static u64 __calc_delta(u64 delta_exec,
  */
 static inline u64 calc_delta_fair(u64 delta, struct sched_entity *se)
 {
-	if (unlikely(se->load.weight != NICE_0_LOAD))
-		delta = __calc_delta(delta, NICE_0_LOAD, &se->load);
+	if (se->h_load.weight != NICE_0_LOAD)
+		delta = __calc_delta(delta, NICE_0_LOAD, &se->h_load);
 
 	return delta;
 }
@@ -427,38 +427,6 @@ static inline struct sched_entity *paren
 	return se->parent;
 }
 
-static void
-find_matching_se(struct sched_entity **se, struct sched_entity **pse)
-{
-	int se_depth, pse_depth;
-
-	/*
-	 * preemption test can be made between sibling entities who are in the
-	 * same cfs_rq i.e who have a common parent. Walk up the hierarchy of
-	 * both tasks until we find their ancestors who are siblings of common
-	 * parent.
-	 */
-
-	/* First walk up until both entities are at same depth */
-	se_depth = (*se)->depth;
-	pse_depth = (*pse)->depth;
-
-	while (se_depth > pse_depth) {
-		se_depth--;
-		*se = parent_entity(*se);
-	}
-
-	while (pse_depth > se_depth) {
-		pse_depth--;
-		*pse = parent_entity(*pse);
-	}
-
-	while (!is_same_group(*se, *pse)) {
-		*se = parent_entity(*se);
-		*pse = parent_entity(*pse);
-	}
-}
-
 static int tg_is_idle(struct task_group *tg)
 {
 	return tg->idle > 0;
@@ -502,11 +470,6 @@ static inline struct sched_entity *paren
 	return NULL;
 }
 
-static inline void
-find_matching_se(struct sched_entity **se, struct sched_entity **pse)
-{
-}
-
 static inline int tg_is_idle(struct task_group *tg)
 {
 	return 0;
@@ -685,7 +648,7 @@ static inline unsigned long avg_vruntime
 static inline void
 __sum_w_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	unsigned long weight = avg_vruntime_weight(cfs_rq, se->load.weight);
+	unsigned long weight = avg_vruntime_weight(cfs_rq, se->h_load.weight);
 	s64 w_vruntime, key = entity_key(cfs_rq, se);
 
 	w_vruntime = key * weight;
@@ -702,7 +665,7 @@ sum_w_vruntime_add_paranoid(struct cfs_r
 	s64 key, tmp;
 
 again:
-	weight = avg_vruntime_weight(cfs_rq, se->load.weight);
+	weight = avg_vruntime_weight(cfs_rq, se->h_load.weight);
 	key = entity_key(cfs_rq, se);
 
 	if (check_mul_overflow(key, weight, &key))
@@ -748,7 +711,7 @@ sum_w_vruntime_add(struct cfs_rq *cfs_rq
 static void
 sum_w_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	unsigned long weight = avg_vruntime_weight(cfs_rq, se->load.weight);
+	unsigned long weight = avg_vruntime_weight(cfs_rq, se->h_load.weight);
 	s64 key = entity_key(cfs_rq, se);
 
 	cfs_rq->sum_w_vruntime -= key * weight;
@@ -790,7 +753,7 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
 		s64 runtime = cfs_rq->sum_w_vruntime;
 
 		if (curr) {
-			unsigned long w = avg_vruntime_weight(cfs_rq, curr->load.weight);
+			unsigned long w = avg_vruntime_weight(cfs_rq, curr->h_load.weight);
 
 			runtime += entity_key(cfs_rq, curr) * w;
 			weight += w;
@@ -861,8 +824,6 @@ bool update_entity_lag(struct cfs_rq *cf
 	u64 avruntime = avg_vruntime(cfs_rq);
 	s64 vlag = entity_lag(cfs_rq, se, avruntime);
 
-	WARN_ON_ONCE(!se->on_rq);
-
 	if (se->sched_delayed) {
 		/* previous vlag < 0 otherwise se would not be delayed */
 		vlag = max(vlag, se->vlag);
@@ -898,7 +859,7 @@ static int vruntime_eligible(struct cfs_
 	long load = cfs_rq->sum_weight;
 
 	if (curr && curr->on_rq) {
-		unsigned long weight = avg_vruntime_weight(cfs_rq, curr->load.weight);
+		unsigned long weight = avg_vruntime_weight(cfs_rq, curr->h_load.weight);
 
 		avg += entity_key(cfs_rq, curr) * weight;
 		load += weight;
@@ -1039,6 +1000,9 @@ RB_DECLARE_CALLBACKS(static, min_vruntim
  */
 static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	WARN_ON_ONCE(&rq_of(cfs_rq)->cfs != cfs_rq);
+	WARN_ON_ONCE(!entity_is_task(se));
+
 	sum_w_vruntime_add(cfs_rq, se);
 	se->min_vruntime = se->vruntime;
 	se->min_slice = se->slice;
@@ -1048,6 +1012,9 @@ static void __enqueue_entity(struct cfs_
 
 static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	WARN_ON_ONCE(&rq_of(cfs_rq)->cfs != cfs_rq);
+	WARN_ON_ONCE(!entity_is_task(se));
+
 	rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
 				  &min_vruntime_cb);
 	sum_w_vruntime_sub(cfs_rq, se);
@@ -1144,7 +1111,7 @@ static struct sched_entity *pick_eevdf(s
 	 * We can safely skip eligibility check if there is only one entity
 	 * in this cfs_rq, saving some cycles.
 	 */
-	if (cfs_rq->nr_queued == 1)
+	if (cfs_rq->h_nr_queued == 1)
 		return curr && curr->on_rq ? curr : se;
 
 	/*
@@ -1391,8 +1358,6 @@ static s64 update_se(struct rq *rq, stru
 	return delta_exec;
 }
 
-static void set_next_buddy(struct sched_entity *se);
-
 /*
  * Used by other classes to account runtime.
  */
@@ -1412,7 +1377,7 @@ static void update_curr(struct cfs_rq *c
 	 * not necessarily be the actual task running
 	 * (rq->curr.se). This is easy to confuse!
 	 */
-	struct sched_entity *curr = cfs_rq->curr;
+	struct sched_entity *curr = cfs_rq->h_curr;
 	struct rq *rq = rq_of(cfs_rq);
 	s64 delta_exec;
 	bool resched;
@@ -1424,26 +1389,29 @@ static void update_curr(struct cfs_rq *c
 	if (unlikely(delta_exec <= 0))
 		return;
 
+	account_cfs_rq_runtime(cfs_rq, delta_exec);
+
+	if (!entity_is_task(curr))
+		return;
+
+	cfs_rq = &rq->cfs;
+
 	curr->vruntime += calc_delta_fair(delta_exec, curr);
 	resched = update_deadline(cfs_rq, curr);
 
-	if (entity_is_task(curr)) {
-		/*
-		 * If the fair_server is active, we need to account for the
-		 * fair_server time whether or not the task is running on
-		 * behalf of fair_server or not:
-		 *  - If the task is running on behalf of fair_server, we need
-		 *    to limit its time based on the assigned runtime.
-		 *  - Fair task that runs outside of fair_server should account
-		 *    against fair_server such that it can account for this time
-		 *    and possibly avoid running this period.
-		 */
-		dl_server_update(&rq->fair_server, delta_exec);
-	}
-
-	account_cfs_rq_runtime(cfs_rq, delta_exec);
+	/*
+	 * If the fair_server is active, we need to account for the
+	 * fair_server time whether or not the task is running on
+	 * behalf of fair_server or not:
+	 *  - If the task is running on behalf of fair_server, we need
+	 *    to limit its time based on the assigned runtime.
+	 *  - Fair task that runs outside of fair_server should account
+	 *    against fair_server such that it can account for this time
+	 *    and possibly avoid running this period.
+	 */
+	dl_server_update(&rq->fair_server, delta_exec);
 
-	if (cfs_rq->nr_queued == 1)
+	if (cfs_rq->h_nr_queued == 1)
 		return;
 
 	if (resched || !protect_slice(curr)) {
@@ -1454,7 +1422,10 @@ static void update_curr(struct cfs_rq *c
 
 static void update_curr_fair(struct rq *rq)
 {
-	update_curr(cfs_rq_of(&rq->donor->se));
+	struct sched_entity *se = &rq->donor->se;
+
+	for_each_sched_entity(se)
+		update_curr(cfs_rq_of(se));
 }
 
 static inline void
@@ -1530,7 +1501,7 @@ update_stats_enqueue_fair(struct cfs_rq
 	 * Are we enqueueing a waiting task? (for current tasks
 	 * a dequeue/enqueue event is a NOP)
 	 */
-	if (se != cfs_rq->curr)
+	if (se != cfs_rq->h_curr)
 		update_stats_wait_start_fair(cfs_rq, se);
 
 	if (flags & ENQUEUE_WAKEUP)
@@ -1548,7 +1519,7 @@ update_stats_dequeue_fair(struct cfs_rq
 	 * Mark the end of the wait period if dequeueing a
 	 * waiting task:
 	 */
-	if (se != cfs_rq->curr)
+	if (se != cfs_rq->h_curr)
 		update_stats_wait_end_fair(cfs_rq, se);
 
 	if ((flags & DEQUEUE_SLEEP) && entity_is_task(se)) {
@@ -3875,6 +3846,7 @@ static inline void update_scan_period(st
 static void
 account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	WARN_ON_ONCE(cfs_rq != cfs_rq_of(se));
 	update_load_add(&cfs_rq->load, se->load.weight);
 	if (entity_is_task(se)) {
 		struct rq *rq = rq_of(cfs_rq);
@@ -3888,6 +3860,7 @@ account_entity_enqueue(struct cfs_rq *cf
 static void
 account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
+	WARN_ON_ONCE(cfs_rq != cfs_rq_of(se));
 	update_load_sub(&cfs_rq->load, se->load.weight);
 	if (entity_is_task(se)) {
 		account_numa_dequeue(rq_of(cfs_rq), task_of(se));
@@ -3965,7 +3938,7 @@ dequeue_load_avg(struct cfs_rq *cfs_rq,
 static void
 rescale_entity(struct sched_entity *se, unsigned long weight, bool rel_vprot)
 {
-	unsigned long old_weight = se->load.weight;
+	long old_weight = se->h_load.weight;
 
 	/*
 	 * VRUNTIME
@@ -4065,16 +4038,17 @@ rescale_entity(struct sched_entity *se,
 		se->vprot = div64_long(se->vprot * old_weight, weight);
 }
 
-static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
-			    unsigned long weight)
+static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
+			   unsigned long weight, bool on_rq)
 {
 	bool curr = cfs_rq->curr == se;
 	bool rel_vprot = false;
 	u64 avruntime = 0;
 
-	if (se->on_rq) {
-		/* commit outstanding execution time */
-		update_curr(cfs_rq);
+	if (se->h_load.weight == weight)
+		return;
+
+	if (on_rq) {
 		avruntime = avg_vruntime(cfs_rq);
 		se->vlag = entity_lag(cfs_rq, se, avruntime);
 		se->deadline -= avruntime;
@@ -4084,46 +4058,90 @@ static void reweight_entity(struct cfs_r
 			rel_vprot = true;
 		}
 
-		cfs_rq->nr_queued--;
+		cfs_rq->h_nr_queued--;
 		if (!curr)
 			__dequeue_entity(cfs_rq, se);
-		update_load_sub(&cfs_rq->load, se->load.weight);
 	}
-	dequeue_load_avg(cfs_rq, se);
 
 	rescale_entity(se, weight, rel_vprot);
 
-	update_load_set(&se->load, weight);
+	update_load_set(&se->h_load, weight);
 
-	do {
-		u32 divider = get_pelt_divider(&se->avg);
-		se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
-	} while (0);
-
-	enqueue_load_avg(cfs_rq, se);
-	if (se->on_rq) {
+	if (on_rq) {
 		if (rel_vprot)
 			se->vprot += avruntime;
 		se->deadline += avruntime;
 		se->rel_deadline = 0;
 		se->vruntime = avruntime - se->vlag;
 
-		update_load_add(&cfs_rq->load, se->load.weight);
 		if (!curr)
 			__enqueue_entity(cfs_rq, se);
-		cfs_rq->nr_queued++;
+		cfs_rq->h_nr_queued++;
 	}
 }
 
+static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
+			    unsigned long weight)
+{
+	if (se->load.weight == weight)
+		return;
+
+	if (se->on_rq) {
+		WARN_ON_ONCE(cfs_rq != cfs_rq_of(se));
+		update_load_sub(&cfs_rq->load, se->load.weight);
+	}
+	dequeue_load_avg(cfs_rq, se);
+
+	update_load_set(&se->load, weight);
+
+	do {
+		u32 divider = get_pelt_divider(&se->avg);
+		se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
+	} while (0);
+
+	enqueue_load_avg(cfs_rq, se);
+
+	if (se->on_rq)
+		update_load_add(&cfs_rq->load, se->load.weight);
+}
+
+/*
+ * weight = NICE_0_LOAD;
+ * for_each_entity_se(se)
+ *   weight = __calc_prop_weight(cfs_rq_of(se), se, weight);
+ */
+static __always_inline
+unsigned long __calc_prop_weight(struct cfs_rq *cfs_rq, struct sched_entity *se,
+				 unsigned long weight)
+{
+	weight *= se->load.weight;
+	if (parent_entity(se))
+		weight /= cfs_rq->load.weight;
+	else
+		weight /= NICE_0_LOAD;
+
+	return max(weight, MIN_SHARES);
+}
+
 static void reweight_task_fair(struct rq *rq, struct task_struct *p,
 			       const struct load_weight *lw)
 {
 	struct sched_entity *se = &p->se;
-	struct cfs_rq *cfs_rq = cfs_rq_of(se);
-	struct load_weight *load = &se->load;
+	unsigned long weight = NICE_0_LOAD;
+
+	if (se->on_rq)
+		update_curr_fair(rq);
+
+	reweight_entity(cfs_rq_of(se), se, lw->weight);
+	se->load.inv_weight = lw->inv_weight;
+
+	if (!se->on_rq)
+		return;
+
+	for_each_sched_entity(se)
+		weight = __calc_prop_weight(cfs_rq_of(se), se, weight);
 
-	reweight_entity(cfs_rq, se, lw->weight);
-	load->inv_weight = lw->inv_weight;
+	reweight_eevdf(&rq->cfs, &p->se, weight, p->se.on_rq);
 }
 
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
@@ -4331,7 +4349,6 @@ static long calc_group_shares(struct cfs
 static void update_cfs_group(struct sched_entity *se)
 {
 	struct cfs_rq *gcfs_rq = group_cfs_rq(se);
-	long shares;
 
 	/*
 	 * When a group becomes empty, preserve its weight. This matters for
@@ -4340,9 +4357,7 @@ static void update_cfs_group(struct sche
 	if (!gcfs_rq || !gcfs_rq->load.weight)
 		return;
 
-	shares = calc_group_shares(gcfs_rq);
-	if (unlikely(se->load.weight != shares))
-		reweight_entity(cfs_rq_of(se), se, shares);
+	reweight_entity(cfs_rq_of(se), se, calc_group_shares(gcfs_rq));
 }
 
 #else /* !CONFIG_FAIR_GROUP_SCHED: */
@@ -4460,7 +4475,7 @@ static inline bool cfs_rq_is_decayed(str
  * differential update where we store the last value we propagated. This in
  * turn allows skipping updates if the differential is 'small'.
  *
- * Updating tg's load_avg is necessary before update_cfs_share().
+ * Updating tg's load_avg is necessary before update_cfs_group().
  */
 static inline void update_tg_load_avg(struct cfs_rq *cfs_rq)
 {
@@ -4926,7 +4941,7 @@ static void migrate_se_pelt_lag(struct s
  * The cfs_rq avg is the direct sum of all its entities (blocked and runnable)
  * avg. The immediate corollary is that all (fair) tasks must be attached.
  *
- * cfs_rq->avg is used for task_h_load() and update_cfs_share() for example.
+ * cfs_rq->avg is used for task_h_load() and update_cfs_group() for example.
  *
  * Return: true if the load decayed or we removed load.
  *
@@ -5475,6 +5490,7 @@ static void
 place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
 	u64 vslice, vruntime = avg_vruntime(cfs_rq);
+	unsigned int nr_queued = cfs_rq->h_nr_queued;
 	bool update_zero = false;
 	s64 lag = 0;
 
@@ -5482,6 +5498,9 @@ place_entity(struct cfs_rq *cfs_rq, stru
 		se->slice = sysctl_sched_base_slice;
 	vslice = calc_delta_fair(se->slice, se);
 
+	if (flags & ENQUEUE_QUEUED)
+		nr_queued -= 1;
+
 	/*
 	 * Due to how V is constructed as the weighted average of entities,
 	 * adding tasks with positive lag, or removing tasks with negative lag
@@ -5490,7 +5509,7 @@ place_entity(struct cfs_rq *cfs_rq, stru
 	 *
 	 * EEVDF: placement strategy #1 / #2
 	 */
-	if (sched_feat(PLACE_LAG) && cfs_rq->nr_queued && se->vlag) {
+	if (sched_feat(PLACE_LAG) && nr_queued && se->vlag) {
 		struct sched_entity *curr = cfs_rq->curr;
 		long load, weight;
 
@@ -5550,9 +5569,9 @@ place_entity(struct cfs_rq *cfs_rq, stru
 		 */
 		load = cfs_rq->sum_weight;
 		if (curr && curr->on_rq)
-			load += avg_vruntime_weight(cfs_rq, curr->load.weight);
+			load += avg_vruntime_weight(cfs_rq, curr->h_load.weight);
 
-		weight = avg_vruntime_weight(cfs_rq, se->load.weight);
+		weight = avg_vruntime_weight(cfs_rq, se->h_load.weight);
 		lag *= load + weight;
 		if (WARN_ON_ONCE(!load))
 			load = 1;
@@ -5611,22 +5630,8 @@ static void check_enqueue_throttle(struc
 static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
 
 static void
-requeue_delayed_entity(struct sched_entity *se);
-
-static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
-	bool curr = cfs_rq->curr == se;
-
-	/*
-	 * If we're the current task, we must renormalise before calling
-	 * update_curr().
-	 */
-	if (curr)
-		place_entity(cfs_rq, se, flags);
-
-	update_curr(cfs_rq);
-
 	/*
 	 * When enqueuing a sched_entity, we must:
 	 *   - Update loads to have both entity and cfs_rq synced with now.
@@ -5645,13 +5650,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 	 */
 	update_cfs_group(se);
 
-	/*
-	 * XXX now that the entity has been re-weighted, and it's lag adjusted,
-	 * we can place the entity.
-	 */
-	if (!curr)
-		place_entity(cfs_rq, se, flags);
-
 	account_entity_enqueue(cfs_rq, se);
 
 	/* Entity has migrated, no longer consider this task hot */
@@ -5660,8 +5658,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 
 	check_schedstat_required();
 	update_stats_enqueue_fair(cfs_rq, se, flags);
-	if (!curr)
-		__enqueue_entity(cfs_rq, se);
 	se->on_rq = 1;
 
 	if (cfs_rq->nr_queued == 1) {
@@ -5679,21 +5675,19 @@ enqueue_entity(struct cfs_rq *cfs_rq, st
 	}
 }
 
-static void __clear_buddies_next(struct sched_entity *se)
+static void set_next_buddy(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
-		if (cfs_rq->next != se)
-			break;
-
-		cfs_rq->next = NULL;
-	}
+	if (WARN_ON_ONCE(!se->on_rq || se->sched_delayed))
+		return;
+	if (se_is_idle(se))
+		return;
+	cfs_rq->next = se;
 }
 
 static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	if (cfs_rq->next == se)
-		__clear_buddies_next(se);
+		cfs_rq->next = NULL;
 }
 
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq);
@@ -5704,7 +5698,7 @@ static void set_delayed(struct sched_ent
 
 	/*
 	 * Delayed se of cfs_rq have no tasks queued on them.
-	 * Do not adjust h_nr_runnable since dequeue_entities()
+	 * Do not adjust h_nr_runnable since __dequeue_task()
 	 * will account it for blocked tasks.
 	 */
 	if (!entity_is_task(se))
@@ -5737,37 +5731,11 @@ static void clear_delayed(struct sched_e
 	}
 }
 
-static bool
+static void
 dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
-	bool sleep = flags & DEQUEUE_SLEEP;
 	int action = UPDATE_TG;
 
-	update_curr(cfs_rq);
-	clear_buddies(cfs_rq, se);
-
-	if (flags & DEQUEUE_DELAYED) {
-		WARN_ON_ONCE(!se->sched_delayed);
-	} else {
-		bool delay = sleep;
-		/*
-		 * DELAY_DEQUEUE relies on spurious wakeups, special task
-		 * states must not suffer spurious wakeups, excempt them.
-		 */
-		if (flags & (DEQUEUE_SPECIAL | DEQUEUE_THROTTLE))
-			delay = false;
-
-		WARN_ON_ONCE(delay && se->sched_delayed);
-
-		if (sched_feat(DELAY_DEQUEUE) && delay &&
-		    !entity_eligible(cfs_rq, se)) {
-			update_load_avg(cfs_rq, se, 0);
-			update_entity_lag(cfs_rq, se);
-			set_delayed(se);
-			return false;
-		}
-	}
-
 	if (entity_is_task(se) && task_on_rq_migrating(task_of(se)))
 		action |= DO_DETACH;
 
@@ -5785,14 +5753,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
 
 	update_stats_dequeue_fair(cfs_rq, se, flags);
 
-	update_entity_lag(cfs_rq, se);
-	if (sched_feat(PLACE_REL_DEADLINE) && !sleep) {
-		se->deadline -= se->vruntime;
-		se->rel_deadline = 1;
-	}
-
-	if (se != cfs_rq->curr)
-		__dequeue_entity(cfs_rq, se);
 	se->on_rq = 0;
 	account_entity_dequeue(cfs_rq, se);
 
@@ -5801,9 +5761,6 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
 
 	update_cfs_group(se);
 
-	if (flags & DEQUEUE_DELAYED)
-		clear_delayed(se);
-
 	if (cfs_rq->nr_queued == 0) {
 		update_idle_cfs_rq_clock_pelt(cfs_rq);
 #ifdef CONFIG_CFS_BANDWIDTH
@@ -5816,15 +5773,11 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
 		}
 #endif
 	}
-
-	return true;
 }
 
 static void
-set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, bool first)
+set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	clear_buddies(cfs_rq, se);
-
 	/* 'current' is not kept within the tree. */
 	if (se->on_rq) {
 		/*
@@ -5833,16 +5786,12 @@ set_next_entity(struct cfs_rq *cfs_rq, s
 		 * runqueue.
 		 */
 		update_stats_wait_end_fair(cfs_rq, se);
-		__dequeue_entity(cfs_rq, se);
 		update_load_avg(cfs_rq, se, UPDATE_TG);
-
-		if (first)
-			set_protect_slice(cfs_rq, se);
 	}
 
 	update_stats_curr_start(cfs_rq, se);
-	WARN_ON_ONCE(cfs_rq->curr);
-	cfs_rq->curr = se;
+	WARN_ON_ONCE(cfs_rq->h_curr);
+	cfs_rq->h_curr = se;
 
 	/*
 	 * Track our maximum slice length, if the CPU's load is at
@@ -5862,23 +5811,17 @@ set_next_entity(struct cfs_rq *cfs_rq, s
 	se->prev_sum_exec_runtime = se->sum_exec_runtime;
 }
 
-static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags);
+static bool __dequeue_task(struct rq *rq, struct task_struct *p, int flags);
 
-/*
- * Pick the next process, keeping these things in mind, in this order:
- * 1) keep things fair between processes/task groups
- * 2) pick the "next" process, since someone really wants that to run
- * 3) pick the "last" process, for cache locality
- * 4) do not run the "skip" process, if something else is available
- */
 static struct sched_entity *
-pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq, bool protect)
+pick_next_entity(struct rq *rq, bool protect)
 {
+	struct cfs_rq *cfs_rq = &rq->cfs;
 	struct sched_entity *se;
 
 	se = pick_eevdf(cfs_rq, protect);
 	if (se->sched_delayed) {
-		dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
+		__dequeue_task(rq, task_of(se), DEQUEUE_SLEEP | DEQUEUE_DELAYED);
 		/*
 		 * Must not reference @se again, see __block_task().
 		 */
@@ -5903,13 +5846,11 @@ static void put_prev_entity(struct cfs_r
 
 	if (prev->on_rq) {
 		update_stats_wait_start_fair(cfs_rq, prev);
-		/* Put 'current' back into the tree. */
-		__enqueue_entity(cfs_rq, prev);
 		/* in !on_rq case, update occurred at dequeue */
 		update_load_avg(cfs_rq, prev, 0);
 	}
-	WARN_ON_ONCE(cfs_rq->curr != prev);
-	cfs_rq->curr = NULL;
+	WARN_ON_ONCE(cfs_rq->h_curr != prev);
+	cfs_rq->h_curr = NULL;
 }
 
 static void
@@ -6062,7 +6003,7 @@ static void __account_cfs_rq_runtime(str
 	 * if we're unable to extend our runtime we resched so that the active
 	 * hierarchy can be throttled
 	 */
-	if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->curr))
+	if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->h_curr))
 		resched_curr(rq_of(cfs_rq));
 }
 
@@ -6420,7 +6361,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cf
 	assert_list_leaf_cfs_rq(rq);
 
 	/* Determine whether we need to wake up potentially idle CPU: */
-	if (rq->curr == rq->idle && rq->cfs.nr_queued)
+	if (rq->curr == rq->idle && rq->cfs.h_nr_queued)
 		resched_curr(rq);
 }
 
@@ -6761,7 +6702,7 @@ static void check_enqueue_throttle(struc
 		return;
 
 	/* an active group must be handled by the update_curr()->put() path */
-	if (!cfs_rq->runtime_enabled || cfs_rq->curr)
+	if (!cfs_rq->runtime_enabled || cfs_rq->h_curr)
 		return;
 
 	/* ensure the group is not already throttled */
@@ -7156,7 +7097,7 @@ static void hrtick_start_fair(struct rq
 			resched_curr(rq);
 		return;
 	}
-	delta = (se->load.weight * vdelta) / NICE_0_LOAD;
+	delta = (se->h_load.weight * vdelta) / NICE_0_LOAD;
 
 	/*
 	 * Correct for instantaneous load of other classes.
@@ -7256,10 +7197,8 @@ static int choose_idle_cpu(int cpu, stru
 }
 
 static void
-requeue_delayed_entity(struct sched_entity *se)
+requeue_delayed_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	struct cfs_rq *cfs_rq = cfs_rq_of(se);
-
 	/*
 	 * se->sched_delayed should imply: se->on_rq == 1.
 	 * Because a delayed entity is one that is still on
@@ -7269,19 +7208,58 @@ requeue_delayed_entity(struct sched_enti
 	WARN_ON_ONCE(!se->on_rq);
 
 	if (update_entity_lag(cfs_rq, se)) {
-		cfs_rq->nr_queued--;
+		cfs_rq->h_nr_queued--;
 		if (se != cfs_rq->curr)
 			__dequeue_entity(cfs_rq, se);
 		place_entity(cfs_rq, se, 0);
 		if (se != cfs_rq->curr)
 			__enqueue_entity(cfs_rq, se);
-		cfs_rq->nr_queued++;
+		cfs_rq->h_nr_queued++;
 	}
 
 	update_load_avg(cfs_rq, se, 0);
 	clear_delayed(se);
 }
 
+static unsigned long enqueue_hierarchy(struct task_struct *p, int flags)
+{
+	unsigned long weight = NICE_0_LOAD;
+	int task_new = !(flags & ENQUEUE_WAKEUP);
+	struct sched_entity *se = &p->se;
+	int h_nr_idle = task_has_idle_policy(p);
+	int h_nr_runnable = 1;
+
+	if (task_new && se->sched_delayed)
+		h_nr_runnable = 0;
+
+	for_each_sched_entity(se) {
+		struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+		update_curr(cfs_rq);
+
+		if (!se->on_rq) {
+			enqueue_entity(cfs_rq, se, flags);
+		} else {
+			update_load_avg(cfs_rq, se, UPDATE_TG);
+			se_update_runnable(se);
+			update_cfs_group(se);
+		}
+
+		cfs_rq->h_nr_runnable += h_nr_runnable;
+		cfs_rq->h_nr_queued++;
+		cfs_rq->h_nr_idle += h_nr_idle;
+
+		if (cfs_rq_is_idle(cfs_rq))
+			h_nr_idle = 1;
+
+		weight = __calc_prop_weight(cfs_rq, se, weight);
+
+		flags = ENQUEUE_WAKEUP;
+	}
+
+	return weight;
+}
+
 /*
  * The enqueue_task method is called before nr_running is
  * increased. Here we update the fair scheduling stats and
@@ -7290,13 +7268,12 @@ requeue_delayed_entity(struct sched_enti
 static void
 enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
-	struct cfs_rq *cfs_rq;
-	struct sched_entity *se = &p->se;
-	int h_nr_idle = task_has_idle_policy(p);
-	int h_nr_runnable = 1;
-	int task_new = !(flags & ENQUEUE_WAKEUP);
 	int rq_h_nr_queued = rq->cfs.h_nr_queued;
-	u64 slice = 0;
+	int task_new = !(flags & ENQUEUE_WAKEUP);
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = &rq->cfs;
+	unsigned long weight;
+	bool curr;
 
 	if (task_is_throttled(p) && enqueue_throttled_task(p))
 		return;
@@ -7308,10 +7285,10 @@ enqueue_task_fair(struct rq *rq, struct
 	 * estimated utilization, before we update schedutil.
 	 */
 	if (!p->se.sched_delayed || (flags & ENQUEUE_DELAYED))
-		util_est_enqueue(&rq->cfs, p);
+		util_est_enqueue(cfs_rq, p);
 
 	if (flags & ENQUEUE_DELAYED) {
-		requeue_delayed_entity(se);
+		requeue_delayed_entity(cfs_rq, se);
 		return;
 	}
 
@@ -7323,57 +7300,22 @@ enqueue_task_fair(struct rq *rq, struct
 	if (p->in_iowait)
 		cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
 
-	if (task_new && se->sched_delayed)
-		h_nr_runnable = 0;
-
-	for_each_sched_entity(se) {
-		if (se->on_rq) {
-			if (se->sched_delayed)
-				requeue_delayed_entity(se);
-			break;
-		}
-		cfs_rq = cfs_rq_of(se);
-
-		/*
-		 * Basically set the slice of group entries to the min_slice of
-		 * their respective cfs_rq. This ensures the group can service
-		 * its entities in the desired time-frame.
-		 */
-		if (slice) {
-			se->slice = slice;
-			se->custom_slice = 1;
-		}
-		enqueue_entity(cfs_rq, se, flags);
-		slice = cfs_rq_min_slice(cfs_rq);
-
-		cfs_rq->h_nr_runnable += h_nr_runnable;
-		cfs_rq->h_nr_queued++;
-		cfs_rq->h_nr_idle += h_nr_idle;
-
-		if (cfs_rq_is_idle(cfs_rq))
-			h_nr_idle = 1;
-
-		flags = ENQUEUE_WAKEUP;
-	}
-
-	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
-
-		update_load_avg(cfs_rq, se, UPDATE_TG);
-		se_update_runnable(se);
-		update_cfs_group(se);
+	/*
+	 * XXX comment on the curr thing
+	 */
+	curr = (cfs_rq->curr == se);
+	if (curr)
+		place_entity(cfs_rq, se, flags);
 
-		se->slice = slice;
-		if (se != cfs_rq->curr)
-			min_vruntime_cb_propagate(&se->run_node, NULL);
-		slice = cfs_rq_min_slice(cfs_rq);
+	if (se->on_rq && se->sched_delayed)
+		requeue_delayed_entity(cfs_rq, se);
 
-		cfs_rq->h_nr_runnable += h_nr_runnable;
-		cfs_rq->h_nr_queued++;
-		cfs_rq->h_nr_idle += h_nr_idle;
+	weight = enqueue_hierarchy(p, flags);
 
-		if (cfs_rq_is_idle(cfs_rq))
-			h_nr_idle = 1;
+	if (!curr) {
+		reweight_eevdf(cfs_rq, se, weight, false);
+		place_entity(cfs_rq, se, flags | ENQUEUE_QUEUED);
+		__enqueue_entity(cfs_rq, se);
 	}
 
 	if (!rq_h_nr_queued && rq->cfs.h_nr_queued)
@@ -7404,105 +7346,107 @@ enqueue_task_fair(struct rq *rq, struct
 	hrtick_update(rq);
 }
 
-/*
- * Basically dequeue_task_fair(), except it can deal with dequeue_entity()
- * failing half-way through and resume the dequeue later.
- *
- * Returns:
- * -1 - dequeue delayed
- *  0 - dequeue throttled
- *  1 - dequeue complete
- */
-static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
+static void dequeue_hierarchy(struct task_struct *p, int flags)
 {
-	bool was_sched_idle = sched_idle_rq(rq);
+	struct sched_entity *se = &p->se;
 	bool task_sleep = flags & DEQUEUE_SLEEP;
 	bool task_delayed = flags & DEQUEUE_DELAYED;
 	bool task_throttled = flags & DEQUEUE_THROTTLE;
-	struct task_struct *p = NULL;
-	int h_nr_idle = 0;
-	int h_nr_queued = 0;
 	int h_nr_runnable = 0;
-	struct cfs_rq *cfs_rq;
-	u64 slice = 0;
+	int h_nr_idle = task_has_idle_policy(p);
+	bool dequeue = true;
 
-	if (entity_is_task(se)) {
-		p = task_of(se);
-		h_nr_queued = 1;
-		h_nr_idle = task_has_idle_policy(p);
-		if (task_sleep || task_delayed || !se->sched_delayed)
-			h_nr_runnable = 1;
-	}
+	if (task_sleep || task_delayed || !se->sched_delayed)
+		h_nr_runnable = 1;
 
 	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
+		struct cfs_rq *cfs_rq = cfs_rq_of(se);
 
-		if (!dequeue_entity(cfs_rq, se, flags)) {
-			if (p && &p->se == se)
-				return -1;
+		update_curr(cfs_rq);
 
-			slice = cfs_rq_min_slice(cfs_rq);
-			break;
+		if (dequeue) {
+			dequeue_entity(cfs_rq, se, flags);
+			/* Don't dequeue parent if it has other entities besides us */
+			if (cfs_rq->load.weight)
+				dequeue = false;
+		} else {
+			update_load_avg(cfs_rq, se, UPDATE_TG);
+			se_update_runnable(se);
+			update_cfs_group(se);
 		}
 
 		cfs_rq->h_nr_runnable -= h_nr_runnable;
-		cfs_rq->h_nr_queued -= h_nr_queued;
+		cfs_rq->h_nr_queued--;
 		cfs_rq->h_nr_idle -= h_nr_idle;
 
 		if (cfs_rq_is_idle(cfs_rq))
-			h_nr_idle = h_nr_queued;
+			h_nr_idle = 1;
 
 		if (throttled_hierarchy(cfs_rq) && task_throttled)
 			record_throttle_clock(cfs_rq);
 
-		/* Don't dequeue parent if it has other entities besides us */
-		if (cfs_rq->load.weight) {
-			slice = cfs_rq_min_slice(cfs_rq);
-
-			/* Avoid re-evaluating load for this entity: */
-			se = parent_entity(se);
-			/*
-			 * Bias pick_next to pick a task from this cfs_rq, as
-			 * p is sleeping when it is within its sched_slice.
-			 */
-			if (task_sleep && se)
-				set_next_buddy(se);
-			break;
-		}
 		flags |= DEQUEUE_SLEEP;
 		flags &= ~(DEQUEUE_DELAYED | DEQUEUE_SPECIAL);
 	}
+}
 
-	for_each_sched_entity(se) {
-		cfs_rq = cfs_rq_of(se);
+/*
+ * The part of dequeue_task_fair() that is needed to dequeue delayed tasks.
+ *
+ * Returns:
+ *   true  - dequeued
+ *   false - delayed
+ */
+static bool __dequeue_task(struct rq *rq, struct task_struct *p, int flags)
+{
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = &rq->cfs;
+	bool was_sched_idle = sched_idle_rq(rq);
+	bool task_sleep = flags & DEQUEUE_SLEEP;
+	bool task_delayed = flags & DEQUEUE_DELAYED;
 
-		update_load_avg(cfs_rq, se, UPDATE_TG);
-		se_update_runnable(se);
-		update_cfs_group(se);
+	clear_buddies(cfs_rq, se);
 
-		se->slice = slice;
-		if (se != cfs_rq->curr)
-			min_vruntime_cb_propagate(&se->run_node, NULL);
-		slice = cfs_rq_min_slice(cfs_rq);
+	if (flags & DEQUEUE_DELAYED) {
+		WARN_ON_ONCE(!se->sched_delayed);
+	} else {
+		bool delay = task_sleep;
+		/*
+		 * DELAY_DEQUEUE relies on spurious wakeups, special task
+		 * states must not suffer spurious wakeups, excempt them.
+		 */
+		if (flags & (DEQUEUE_SPECIAL | DEQUEUE_THROTTLE))
+			delay = false;
 
-		cfs_rq->h_nr_runnable -= h_nr_runnable;
-		cfs_rq->h_nr_queued -= h_nr_queued;
-		cfs_rq->h_nr_idle -= h_nr_idle;
+		WARN_ON_ONCE(delay && se->sched_delayed);
 
-		if (cfs_rq_is_idle(cfs_rq))
-			h_nr_idle = h_nr_queued;
+		if (sched_feat(DELAY_DEQUEUE) && delay &&
+		    !entity_eligible(cfs_rq, se)) {
+			update_load_avg(cfs_rq_of(se), se, 0);
+			set_delayed(se);
+			return false;
+		}
+	}
 
-		if (throttled_hierarchy(cfs_rq) && task_throttled)
-			record_throttle_clock(cfs_rq);
+	dequeue_hierarchy(p, flags);
+
+	update_entity_lag(cfs_rq, se);
+	if (sched_feat(PLACE_REL_DEADLINE) && !task_sleep) {
+		se->deadline -= se->vruntime;
+		se->rel_deadline = 1;
 	}
+	if (se != cfs_rq->curr)
+		__dequeue_entity(cfs_rq, se);
 
-	sub_nr_running(rq, h_nr_queued);
+	sub_nr_running(rq, 1);
 
 	/* balance early to pull high priority tasks */
 	if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
 		rq->next_balance = jiffies;
 
-	if (p && task_delayed) {
+	if (task_delayed) {
+		clear_delayed(se);
+
 		WARN_ON_ONCE(!task_sleep);
 		WARN_ON_ONCE(p->on_rq != 1);
 
@@ -7514,7 +7458,7 @@ static int dequeue_entities(struct rq *r
 		__block_task(rq, p);
 	}
 
-	return 1;
+	return true;
 }
 
 /*
@@ -7533,11 +7477,11 @@ static bool dequeue_task_fair(struct rq
 		util_est_dequeue(&rq->cfs, p);
 
 	util_est_update(&rq->cfs, p, flags & DEQUEUE_SLEEP);
-	if (dequeue_entities(rq, &p->se, flags) < 0)
+	if (!__dequeue_task(rq, p, flags))
 		return false;
 
 	/*
-	 * Must not reference @p after dequeue_entities(DEQUEUE_DELAYED).
+	 * Must not reference @p after __dequeue_task(DEQUEUE_DELAYED).
 	 */
 	return true;
 }
@@ -9021,19 +8965,6 @@ static void migrate_task_rq_fair(struct
 static void task_dead_fair(struct task_struct *p)
 {
 	struct sched_entity *se = &p->se;
-
-	if (se->sched_delayed) {
-		struct rq_flags rf;
-		struct rq *rq;
-
-		rq = task_rq_lock(p, &rf);
-		if (se->sched_delayed) {
-			update_rq_clock(rq);
-			dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
-		}
-		task_rq_unlock(rq, p, &rf);
-	}
-
 	remove_entity_load_avg(se);
 }
 
@@ -9067,21 +8998,10 @@ static void set_cpus_allowed_fair(struct
 	set_task_max_allowed_capacity(p);
 }
 
-static void set_next_buddy(struct sched_entity *se)
-{
-	for_each_sched_entity(se) {
-		if (WARN_ON_ONCE(!se->on_rq))
-			return;
-		if (se_is_idle(se))
-			return;
-		cfs_rq_of(se)->next = se;
-	}
-}
-
 enum preempt_wakeup_action {
 	PREEMPT_WAKEUP_NONE,	/* No preemption. */
 	PREEMPT_WAKEUP_SHORT,	/* Ignore slice protection. */
-	PREEMPT_WAKEUP_PICK,	/* Let __pick_eevdf() decide. */
+	PREEMPT_WAKEUP_PICK,	/* Let pick_eevdf() decide. */
 	PREEMPT_WAKEUP_RESCHED,	/* Force reschedule. */
 };
 
@@ -9098,7 +9018,7 @@ set_preempt_buddy(struct cfs_rq *cfs_rq,
 	if (cfs_rq->next && entity_before(cfs_rq->next, pse))
 		return false;
 
-	set_next_buddy(pse);
+	set_next_buddy(cfs_rq, pse);
 	return true;
 }
 
@@ -9188,7 +9108,6 @@ static void wakeup_preempt_fair(struct r
 	if (!sched_feat(WAKEUP_PREEMPTION))
 		return;
 
-	find_matching_se(&se, &pse);
 	WARN_ON_ONCE(!pse);
 
 	cse_is_idle = se_is_idle(se);
@@ -9216,8 +9135,7 @@ static void wakeup_preempt_fair(struct r
 	if (unlikely(!normal_policy(p->policy)))
 		return;
 
-	cfs_rq = cfs_rq_of(se);
-	update_curr(cfs_rq);
+	update_curr_fair(rq);
 	/*
 	 * If @p has a shorter slice than current and @p is eligible, override
 	 * current's slice protection in order to allow preemption.
@@ -9261,18 +9179,15 @@ static void wakeup_preempt_fair(struct r
 	}
 
 pick:
-	nse = pick_next_entity(rq, cfs_rq, preempt_action != PREEMPT_WAKEUP_SHORT);
-	/* If @p has become the most eligible task, force preemption */
-	if (nse == pse)
-		goto preempt;
-
-	/*
-	 * Because p is enqueued, nse being null can only mean that we
-	 * dequeued a delayed task. If there are still entities queued in
-	 * cfs, check if the next one will be p.
-	 */
-	if (!nse && cfs_rq->nr_queued)
-		goto pick;
+	if (cfs_rq->h_nr_queued) {
+		nse = pick_next_entity(rq, preempt_action != PREEMPT_WAKEUP_SHORT);
+		if (unlikely(!nse))
+			goto pick;
+
+		/* If @p has become the most eligible task, force preemption */
+		if (nse == pse)
+			goto preempt;
+	}
 
 	if (sched_feat(RUN_TO_PARITY))
 		update_protect_slice(cfs_rq, se);
@@ -9291,34 +9206,25 @@ static void wakeup_preempt_fair(struct r
 struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
 	__must_hold(__rq_lockp(rq))
 {
+	struct cfs_rq *cfs_rq = &rq->cfs;
 	struct sched_entity *se;
-	struct cfs_rq *cfs_rq;
 	struct task_struct *p;
-	bool throttled;
 	int new_tasks;
 
 again:
-	cfs_rq = &rq->cfs;
-	if (!cfs_rq->nr_queued)
+	if (!cfs_rq->h_nr_queued)
 		goto idle;
 
-	throttled = false;
-
-	do {
-		/* Might not have done put_prev_entity() */
-		if (cfs_rq->curr && cfs_rq->curr->on_rq)
-			update_curr(cfs_rq);
-
-		throttled |= check_cfs_rq_runtime(cfs_rq);
+	/* Might not have done put_prev_entity() */
+	if (cfs_rq->curr && cfs_rq->curr->on_rq)
+		update_curr(cfs_rq);
 
-		se = pick_next_entity(rq, cfs_rq, true);
-		if (!se)
-			goto again;
-		cfs_rq = group_cfs_rq(se);
-	} while (cfs_rq);
+	se = pick_next_entity(rq, true);
+	if (!se)
+		goto again;
 
 	p = task_of(se);
-	if (unlikely(throttled))
+	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
 		task_throttle_setup_work(p);
 	return p;
 
@@ -9353,7 +9259,7 @@ void fair_server_init(struct rq *rq)
 static void put_prev_task_fair(struct rq *rq, struct task_struct *prev, struct task_struct *next)
 {
 	struct sched_entity *se = &prev->se;
-	struct cfs_rq *cfs_rq;
+	struct cfs_rq *cfs_rq = &rq->cfs;
 	struct sched_entity *nse = NULL;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -9363,7 +9269,7 @@ static void put_prev_task_fair(struct rq
 
 	while (se) {
 		cfs_rq = cfs_rq_of(se);
-		if (!nse || cfs_rq->curr)
+		if (!nse || cfs_rq->h_curr)
 			put_prev_entity(cfs_rq, se);
 #ifdef CONFIG_FAIR_GROUP_SCHED
 		if (nse) {
@@ -9382,6 +9288,14 @@ static void put_prev_task_fair(struct rq
 #endif
 		se = parent_entity(se);
 	}
+
+	/* Put 'current' back into the tree. */
+	cfs_rq = &rq->cfs;
+	se = &prev->se;
+	WARN_ON_ONCE(cfs_rq->curr != se);
+	cfs_rq->curr = NULL;
+	if (se->on_rq)
+		__enqueue_entity(cfs_rq, se);
 }
 
 /*
@@ -9390,8 +9304,8 @@ static void put_prev_task_fair(struct rq
 static void yield_task_fair(struct rq *rq)
 {
 	struct task_struct *curr = rq->donor;
-	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
 	struct sched_entity *se = &curr->se;
+	struct cfs_rq *cfs_rq = &rq->cfs;
 
 	/*
 	 * Are we the only task in the tree?
@@ -9432,11 +9346,11 @@ static bool yield_to_task_fair(struct rq
 	struct sched_entity *se = &p->se;
 
 	/* !se->on_rq also covers throttled task */
-	if (!se->on_rq)
+	if (!se->on_rq || se->sched_delayed)
 		return false;
 
 	/* Tell the scheduler that we'd really like se to run next. */
-	set_next_buddy(se);
+	set_next_buddy(&task_rq(p)->cfs, se);
 
 	yield_task_fair(rq);
 
@@ -9762,15 +9676,10 @@ static inline long migrate_degrades_loca
  */
 static inline int task_is_ineligible_on_dst_cpu(struct task_struct *p, int dest_cpu)
 {
-	struct cfs_rq *dst_cfs_rq;
+	struct cfs_rq *dst_cfs_rq = &cpu_rq(dest_cpu)->cfs;
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	dst_cfs_rq = task_group(p)->cfs_rq[dest_cpu];
-#else
-	dst_cfs_rq = &cpu_rq(dest_cpu)->cfs;
-#endif
-	if (sched_feat(PLACE_LAG) && dst_cfs_rq->nr_queued &&
-	    !entity_eligible(task_cfs_rq(p), &p->se))
+	if (sched_feat(PLACE_LAG) && dst_cfs_rq->h_nr_queued &&
+	    !entity_eligible(&task_rq(p)->cfs, &p->se))
 		return 1;
 
 	return 0;
@@ -10240,7 +10149,7 @@ static void update_cfs_rq_h_load(struct
 	while ((se = READ_ONCE(cfs_rq->h_load_next)) != NULL) {
 		load = cfs_rq->h_load;
 		load = div64_ul(load * se->avg.load_avg,
-			cfs_rq_load_avg(cfs_rq) + 1);
+				cfs_rq_load_avg(cfs_rq) + 1);
 		cfs_rq = group_cfs_rq(se);
 		cfs_rq->h_load = load;
 		cfs_rq->last_h_load_update = now;
@@ -13459,7 +13368,7 @@ static inline void task_tick_core(struct
 	 * MIN_NR_TASKS_DURING_FORCEIDLE - 1 tasks and use that to check
 	 * if we need to give up the CPU.
 	 */
-	if (rq->core->core_forceidle_count && rq->cfs.nr_queued == 1 &&
+	if (rq->core->core_forceidle_count && rq->cfs.h_nr_queued == 1 &&
 	    __entity_slice_used(&curr->se, MIN_NR_TASKS_DURING_FORCEIDLE))
 		resched_curr(rq);
 }
@@ -13668,30 +13577,8 @@ bool cfs_prio_less(const struct task_str
 
 	WARN_ON_ONCE(task_rq(b)->core != rq->core);
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-	/*
-	 * Find an se in the hierarchy for tasks a and b, such that the se's
-	 * are immediate siblings.
-	 */
-	while (sea->cfs_rq->tg != seb->cfs_rq->tg) {
-		int sea_depth = sea->depth;
-		int seb_depth = seb->depth;
-
-		if (sea_depth >= seb_depth)
-			sea = parent_entity(sea);
-		if (sea_depth <= seb_depth)
-			seb = parent_entity(seb);
-	}
-
-	se_fi_update(sea, rq->core->core_forceidle_seq, in_fi);
-	se_fi_update(seb, rq->core->core_forceidle_seq, in_fi);
-
-	cfs_rqa = sea->cfs_rq;
-	cfs_rqb = seb->cfs_rq;
-#else /* !CONFIG_FAIR_GROUP_SCHED: */
 	cfs_rqa = &task_rq(a)->cfs;
 	cfs_rqb = &task_rq(b)->cfs;
-#endif /* !CONFIG_FAIR_GROUP_SCHED */
 
 	/*
 	 * Find delta after normalizing se's vruntime with its cfs_rq's
@@ -13729,14 +13616,20 @@ static inline void task_tick_core(struct
  */
 static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
 {
-	struct cfs_rq *cfs_rq;
 	struct sched_entity *se = &curr->se;
+	unsigned long weight = NICE_0_LOAD;
+	struct cfs_rq *cfs_rq;
 
 	for_each_sched_entity(se) {
 		cfs_rq = cfs_rq_of(se);
 		entity_tick(cfs_rq, se, queued);
+
+		weight = __calc_prop_weight(cfs_rq, se, weight);
 	}
 
+	se = &curr->se;
+	reweight_eevdf(cfs_rq, se, weight, se->on_rq);
+
 	if (queued)
 		return;
 
@@ -13772,7 +13665,7 @@ prio_changed_fair(struct rq *rq, struct
 	if (p->prio == oldprio)
 		return;
 
-	if (rq->cfs.nr_queued == 1)
+	if (rq->cfs.h_nr_queued == 1)
 		return;
 
 	/*
@@ -13901,29 +13794,40 @@ static void switched_to_fair(struct rq *
 	}
 }
 
-/*
- * Account for a task changing its policy or group.
- *
- * This routine is mostly called to set cfs_rq->curr field when a task
- * migrates between groups/classes.
- */
 static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 {
 	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = &rq->cfs;
+	unsigned long weight = NICE_0_LOAD;
+	bool on_rq = se->on_rq;
+
+	clear_buddies(cfs_rq, se);
+
+	if (on_rq)
+		__dequeue_entity(cfs_rq, se);
 
 	for_each_sched_entity(se) {
-		struct cfs_rq *cfs_rq = cfs_rq_of(se);
+		cfs_rq = cfs_rq_of(se);
 
-		if (IS_ENABLED(CONFIG_FAIR_GROUP_SCHED) &&
-		    first && cfs_rq->curr)
-			break;
+		if (!IS_ENABLED(CONFIG_FAIR_GROUP_SCHED) ||
+		    !first || !cfs_rq->h_curr)
+			set_next_entity(cfs_rq, se);
 
-		set_next_entity(cfs_rq, se, first);
 		/* ensure bandwidth has been allocated on our new cfs_rq */
 		account_cfs_rq_runtime(cfs_rq, 0);
+
+		if (on_rq)
+			weight = __calc_prop_weight(cfs_rq, se, weight);
 	}
 
 	se = &p->se;
+	cfs_rq->curr = se;
+
+	if (on_rq) {
+		reweight_eevdf(cfs_rq, se, weight, se->on_rq);
+		if (first)
+			set_protect_slice(cfs_rq, se);
+	}
 
 	if (task_on_rq_queued(p)) {
 		/*
@@ -14054,17 +13958,8 @@ void unregister_fair_sched_group(struct
 		struct sched_entity *se = tg->se[cpu];
 		struct rq *rq = cpu_rq(cpu);
 
-		if (se) {
-			if (se->sched_delayed) {
-				guard(rq_lock_irqsave)(rq);
-				if (se->sched_delayed) {
-					update_rq_clock(rq);
-					dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
-				}
-				list_del_leaf_cfs_rq(cfs_rq);
-			}
+		if (se)
 			remove_entity_load_avg(se);
-		}
 
 		/*
 		 * Only empty task groups can be destroyed; so we can speculatively
--- a/kernel/sched/pelt.c
+++ b/kernel/sched/pelt.c
@@ -206,7 +206,7 @@ ___update_load_sum(u64 now, struct sched
 	/*
 	 * running is a subset of runnable (weight) so running can't be set if
 	 * runnable is clear. But there are some corner cases where the current
-	 * se has been already dequeued but cfs_rq->curr still points to it.
+	 * se has been already dequeued but cfs_rq->h_curr still points to it.
 	 * This means that weight will be 0 but not running for a sched_entity
 	 * but also for a cfs_rq if the latter becomes idle. As an example,
 	 * this happens during sched_balance_newidle() which calls
@@ -307,7 +307,7 @@ int __update_load_avg_blocked_se(u64 now
 int __update_load_avg_se(u64 now, struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	if (___update_load_sum(now, &se->avg, !!se->on_rq, se_runnable(se),
-				cfs_rq->curr == se)) {
+				cfs_rq->h_curr == se)) {
 
 		___update_load_avg(&se->avg, se_weight(se));
 		cfs_se_util_change(&se->avg);
@@ -323,7 +323,7 @@ int __update_load_avg_cfs_rq(u64 now, st
 	if (___update_load_sum(now, &cfs_rq->avg,
 				scale_load_down(cfs_rq->load.weight),
 				cfs_rq->h_nr_runnable,
-				cfs_rq->curr != NULL)) {
+				cfs_rq->h_curr != NULL)) {
 
 		___update_load_avg(&cfs_rq->avg, 1);
 		trace_pelt_cfs_tp(cfs_rq);
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -528,21 +528,8 @@ struct task_group {
 
 };
 
-#ifdef CONFIG_GROUP_SCHED_WEIGHT
 #define ROOT_TASK_GROUP_LOAD	NICE_0_LOAD
 
-/*
- * A weight of 0 or 1 can cause arithmetics problems.
- * A weight of a cfs_rq is the sum of weights of which entities
- * are queued on this cfs_rq, so a weight of a entity should not be
- * too large, so as the shares value of a task group.
- * (The default weight is 1024 - so there's no practical
- *  limitation from this.)
- */
-#define MIN_SHARES		(1UL <<  1)
-#define MAX_SHARES		(1UL << 18)
-#endif
-
 typedef int (*tg_visitor)(struct task_group *, void *);
 
 extern int walk_tg_tree_from(struct task_group *from,
@@ -629,6 +616,17 @@ static inline bool cfs_task_bw_constrain
 
 #endif /* !CONFIG_CGROUP_SCHED */
 
+/*
+ * A weight of 0 or 1 can cause arithmetics problems.
+ * A weight of a cfs_rq is the sum of weights of which entities
+ * are queued on this cfs_rq, so a weight of a entity should not be
+ * too large, so as the shares value of a task group.
+ * (The default weight is 1024 - so there's no practical
+ *  limitation from this.)
+ */
+#define MIN_SHARES		(1UL <<  1)
+#define MAX_SHARES		(1UL << 18)
+
 extern void unregister_rt_sched_group(struct task_group *tg);
 extern void free_rt_sched_group(struct task_group *tg);
 extern int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent);
@@ -707,6 +705,7 @@ struct cfs_rq {
 	/*
 	 * CFS load tracking
 	 */
+	struct sched_entity	*h_curr;
 	struct sched_avg	avg;
 #ifndef CONFIG_64BIT
 	u64			last_update_time_copy;
@@ -2509,6 +2508,7 @@ extern const u32		sched_prio_to_wmult[40
 #define ENQUEUE_MIGRATED	0x00040000
 #define ENQUEUE_INITIAL		0x00080000
 #define ENQUEUE_RQ_SELECTED	0x00100000
+#define ENQUEUE_QUEUED		0x00200000
 
 #define RETRY_TASK		((void *)-1UL)
 

Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[K Prateek Nayak]

Hello Peter,

On 5/11/2026 5:01 PM, Peter Zijlstra wrote:
> @@ -9291,34 +9206,25 @@ static void wakeup_preempt_fair(struct r
> +	se = pick_next_entity(rq, true);
> +	if (!se)
> +		goto again;
>  
>  	p = task_of(se);
> -	if (unlikely(throttled))
> +	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
>  		task_throttle_setup_work(p);

I think this bit should also be replicated in set_next_task() after
account_cfs_rq_runtime() since any part of the hierarchy may get
throttled as a result of failing to grab runtime.

Also check_cfs_rq_runtime() only sees if the cfs_rq is throttled
but the task can fail to run if it is on a throttled_hierarchy() too
so that should be the correct check here.

Something like below (only build tested on queue/sched/flat):

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e54da4c6c945..950c072244b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9224,7 +9224,19 @@ struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
 		goto again;
 
 	p = task_of(se);
-	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
+	/*
+	 * For cases where prev is picked again after
+	 * being throttled, entity_tick() would have
+	 * already marked its hierarchy as throttled.
+	 *
+	 * Add throttle work here since
+	 * put_prev_set_next_task() is skipped on
+	 * same task's selection.
+	 *
+	 * For other case, set_next_task_fair() will
+	 * handle adding the throttle work.
+	 */
+	if (throttled_hierarchy(cfs_rq_of(se)))
 		task_throttle_setup_work(p);
 	return p;
 
@@ -13819,6 +13831,12 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
 		if (on_rq)
 			weight = __calc_prop_weight(cfs_rq, se, weight);
 	}
+	/*
+	 * Add throttle work if the bandwidth allocation above failed
+	 * to grab any runtime and throttled the task's hierarchy.
+	 */
+	if (throttled_hierarchy(task_cfs_rq(p)))
+		task_throttle_setup_work(p);
 
 	se = &p->se;
 	cfs_rq->curr = se;
---


>  	return p;
>  

-- 
Thanks and Regards,
Prateek

Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[Peter Zijlstra]

On Mon, May 11, 2026 at 09:51:57PM +0530, K Prateek Nayak wrote:
> Hello Peter,
> 
> On 5/11/2026 5:01 PM, Peter Zijlstra wrote:
> > @@ -9291,34 +9206,25 @@ static void wakeup_preempt_fair(struct r
> > +	se = pick_next_entity(rq, true);
> > +	if (!se)
> > +		goto again;
> >  
> >  	p = task_of(se);
> > -	if (unlikely(throttled))
> > +	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
> >  		task_throttle_setup_work(p);
> 
> I think this bit should also be replicated in set_next_task() after
> account_cfs_rq_runtime() since any part of the hierarchy may get
> throttled as a result of failing to grab runtime.
> 
> Also check_cfs_rq_runtime() only sees if the cfs_rq is throttled
> but the task can fail to run if it is on a throttled_hierarchy() too
> so that should be the correct check here.
> 
> Something like below (only build tested on queue/sched/flat):
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e54da4c6c945..950c072244b2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9224,7 +9224,19 @@ struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
>  		goto again;
>  
>  	p = task_of(se);
> -	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
> +	/*
> +	 * For cases where prev is picked again after
> +	 * being throttled, entity_tick() would have
> +	 * already marked its hierarchy as throttled.
> +	 *
> +	 * Add throttle work here since
> +	 * put_prev_set_next_task() is skipped on
> +	 * same task's selection.
> +	 *
> +	 * For other case, set_next_task_fair() will
> +	 * handle adding the throttle work.
> +	 */
> +	if (throttled_hierarchy(cfs_rq_of(se)))
>  		task_throttle_setup_work(p);

Ah, right, because we've not accumulated runtime, it doesn't make sense
to use check_cfs_rq_runtime() at pick time, all we need to do is check
if the task should be throttled.

However, since set_next_task_fair() will walk the entire hierarchy
anyway, we can remove it here entirely and fully rely on that.

>  	return p;
>  
> @@ -13819,6 +13831,12 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first)
>  		if (on_rq)
>  			weight = __calc_prop_weight(cfs_rq, se, weight);
>  	}
> +	/*
> +	 * Add throttle work if the bandwidth allocation above failed
> +	 * to grab any runtime and throttled the task's hierarchy.
> +	 */
> +	if (throttled_hierarchy(task_cfs_rq(p)))
> +		task_throttle_setup_work(p);

We already call into account_cfs_rq_runtime(); which basically does all
we need.

I think the distinction between account_cfs_rq_runtime() and
check_cfs_rq_runtime() no longer makes sense. We can throttle a cfs_rq
at any point now, since we no longer remove the cfs_rq, but rather we
make the tasks suspend themselves until the cfs_rq naturally dequeues
for being empty.

Something like so perhaps?

---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -488,7 +488,7 @@ static int se_is_idle(struct sched_entit
 #endif /* !CONFIG_FAIR_GROUP_SCHED */
 
 static __always_inline
-void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);
+bool account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec);
 
 /**************************************************************
  * Scheduling class tree data structure manipulation methods:
@@ -1420,12 +1420,22 @@ static void update_curr(struct cfs_rq *c
 	}
 }
 
+static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
+static inline void task_throttle_setup_work(struct task_struct *p);
+
 static void update_curr_fair(struct rq *rq)
 {
 	struct sched_entity *se = &rq->donor->se;
+	bool throttled = false;
 
-	for_each_sched_entity(se)
-		update_curr(cfs_rq_of(se));
+	for_each_sched_entity(se) {
+		struct cfs_rq *cfs_rq = cfs_rq_of(se);
+		update_curr(cfs_rq);
+		throttled |= cfs_rq_throttled(cfs_rq);
+	}
+
+	if (throttled)
+		task_throttle_setup_work(rq->donor);
 }
 
 static inline void
@@ -5627,7 +5637,6 @@ place_entity(struct cfs_rq *cfs_rq, stru
 }
 
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq);
-static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
 
 static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
@@ -5830,8 +5839,6 @@ pick_next_entity(struct rq *rq, bool pro
 	return se;
 }
 
-static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq);
-
 static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev)
 {
 	/*
@@ -5841,9 +5848,6 @@ static void put_prev_entity(struct cfs_r
 	if (prev->on_rq)
 		update_curr(cfs_rq);
 
-	/* throttle cfs_rqs exceeding runtime */
-	check_cfs_rq_runtime(cfs_rq);
-
 	if (prev->on_rq) {
 		update_stats_wait_start_fair(cfs_rq, prev);
 		/* in !on_rq case, update occurred at dequeue */
@@ -5976,44 +5980,29 @@ static int __assign_cfs_rq_runtime(struc
 	return cfs_rq->runtime_remaining > 0;
 }
 
-/* returns 0 on failure to allocate runtime */
-static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
-{
-	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
-	int ret;
-
-	raw_spin_lock(&cfs_b->lock);
-	ret = __assign_cfs_rq_runtime(cfs_b, cfs_rq, sched_cfs_bandwidth_slice());
-	raw_spin_unlock(&cfs_b->lock);
-
-	return ret;
-}
+static bool throttle_cfs_rq(struct cfs_rq *cfs_rq);
 
-static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
+static bool __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 {
 	/* dock delta_exec before expiring quota (as it could span periods) */
 	cfs_rq->runtime_remaining -= delta_exec;
 
 	if (likely(cfs_rq->runtime_remaining > 0))
-		return;
+		return false;
 
 	if (cfs_rq->throttled)
-		return;
-	/*
-	 * if we're unable to extend our runtime we resched so that the active
-	 * hierarchy can be throttled
-	 */
-	if (!assign_cfs_rq_runtime(cfs_rq) && likely(cfs_rq->h_curr))
-		resched_curr(rq_of(cfs_rq));
+		return true;
+
+	return throttle_cfs_rq(cfs_rq);
 }
 
 static __always_inline
-void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
+bool account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 {
 	if (!cfs_bandwidth_used() || !cfs_rq->runtime_enabled)
-		return;
+		return false;
 
-	__account_cfs_rq_runtime(cfs_rq, delta_exec);
+	return __account_cfs_rq_runtime(cfs_rq, delta_exec);
 }
 
 static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
@@ -6284,9 +6273,9 @@ static bool throttle_cfs_rq(struct cfs_r
 		 * We have raced with bandwidth becoming available, and if we
 		 * actually throttled the timer might not unthrottle us for an
 		 * entire period. We additionally needed to make sure that any
-		 * subsequent check_cfs_rq_runtime calls agree not to throttle
-		 * us, as we may commit to do cfs put_prev+pick_next, so we ask
-		 * for 1ns of runtime rather than just check cfs_b.
+		 * subsequent account_cfs_rq_runtime() calls agree not to
+		 * throttle us, as we may commit to do cfs put_prev+pick_next,
+		 * so we ask for 1ns of runtime rather than just check cfs_b.
 		 */
 		dequeue = 0;
 	} else {
@@ -6711,8 +6700,6 @@ static void check_enqueue_throttle(struc
 
 	/* update runtime allocation */
 	account_cfs_rq_runtime(cfs_rq, 0);
-	if (cfs_rq->runtime_remaining <= 0)
-		throttle_cfs_rq(cfs_rq);
 }
 
 static void sync_throttle(struct task_group *tg, int cpu)
@@ -6742,25 +6729,6 @@ static void sync_throttle(struct task_gr
 		cfs_rq->pelt_clock_throttled = 1;
 }
 
-/* conditionally throttle active cfs_rq's from put_prev_entity() */
-static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
-{
-	if (!cfs_bandwidth_used())
-		return false;
-
-	if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0))
-		return false;
-
-	/*
-	 * it's possible for a throttled entity to be forced into a running
-	 * state (e.g. set_curr_task), in this case we're finished.
-	 */
-	if (cfs_rq_throttled(cfs_rq))
-		return true;
-
-	return throttle_cfs_rq(cfs_rq);
-}
-
 static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer)
 {
 	struct cfs_bandwidth *cfs_b =
@@ -7015,8 +6983,7 @@ static void sched_fair_update_stop_tick(
 
 #else /* !CONFIG_CFS_BANDWIDTH: */
 
-static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {}
-static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; }
+static bool account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) { return false; }
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {}
 static inline void sync_throttle(struct task_group *tg, int cpu) {}
 static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
@@ -9208,7 +9175,6 @@ struct task_struct *pick_task_fair(struc
 {
 	struct cfs_rq *cfs_rq = &rq->cfs;
 	struct sched_entity *se;
-	struct task_struct *p;
 	int new_tasks;
 
 again:
@@ -9223,10 +9189,7 @@ struct task_struct *pick_task_fair(struc
 	if (!se)
 		goto again;
 
-	p = task_of(se);
-	if (unlikely(check_cfs_rq_runtime(cfs_rq_of(se))))
-		task_throttle_setup_work(p);
-	return p;
+	return task_of(se);
 
 idle:
 	new_tasks = sched_balance_newidle(rq, rf);
@@ -13618,6 +13581,7 @@ static void task_tick_fair(struct rq *rq
 {
 	struct sched_entity *se = &curr->se;
 	unsigned long weight = NICE_0_LOAD;
+	bool throttled = false;
 	struct cfs_rq *cfs_rq;
 
 	for_each_sched_entity(se) {
@@ -13625,8 +13589,13 @@ static void task_tick_fair(struct rq *rq
 		entity_tick(cfs_rq, se, queued);
 
 		weight = __calc_prop_weight(cfs_rq, se, weight);
+
+		throttled |= cfs_rq_throttled(cfs_rq);
 	}
 
+	if (throttled)
+		task_throttle_setup_work(curr);
+
 	se = &curr->se;
 	reweight_eevdf(cfs_rq, se, weight, se->on_rq);
 
@@ -13800,6 +13769,7 @@ static void set_next_task_fair(struct rq
 	struct cfs_rq *cfs_rq = &rq->cfs;
 	unsigned long weight = NICE_0_LOAD;
 	bool on_rq = se->on_rq;
+	bool throttled = false;
 
 	clear_buddies(cfs_rq, se);
 
@@ -13814,12 +13784,15 @@ static void set_next_task_fair(struct rq
 			set_next_entity(cfs_rq, se);
 
 		/* ensure bandwidth has been allocated on our new cfs_rq */
-		account_cfs_rq_runtime(cfs_rq, 0);
+		throttled |= account_cfs_rq_runtime(cfs_rq, 0);
 
 		if (on_rq)
 			weight = __calc_prop_weight(cfs_rq, se, weight);
 	}
 
+	if (throttled)
+		task_throttle_setup_work(p);
+
 	se = &p->se;
 	cfs_rq->curr = se;
 

Re: [PATCH v2 00/10] sched: Flatten the pick

[Tejun Heo]

Hello, Peter.

On Mon, May 11, 2026 at 01:31:04PM +0200, Peter Zijlstra wrote:
> So cgroup scheduling has always been a pain in the arse. The problems start
> with weight distribution and end with hierachical picks and it all sucks.
> 
> The problems with weight distribution are related to that infernal global
> fraction:
> 
>              tg->w * grq_i->w
>    ge_i->w = ----------------
>              \Sum_j grq_j->w
> 
> which we've approximated reasonably well by now. However, the immediate
> consequence of this fraction is that the total group weight (tg->w) gets
> fragmented across all your CPUs. And at 64 CPUs that means your per-cpu cgroup
> weight ends up being a nice 19 task worth. And more CPUs more tiny. Combine
> with the fact that 256 CPU systems are relatively common these days, this
> becomes painful.
> 
> The common 'solution' is to inflate the group weight by 'nr_cpus'; the
> immediate problem with that is that when all load of a group gets concentrated
> on a single CPU, the per-cpu cgroup weight becomes insanely large, easily
> exceeding nice -20.
> 
> Additionally there are numerical limits on the max weight you can have before
> the math starts suffering overflows. As such there is a definite limit on the
> total group weight. Which has annoyed people ;-)
> 
> The first few patches add a knob /debug/sched/cgroup_mode and a few different
> options on how to deal with this. My favourite is 'concur', but obviously that
> is also the most expensive one :-/ It adds a tg->tasks counter which makes the
> update_tg_load_avg() thing more expensive.

Ignoring fixed math accuracy problems, isn't the root problem here that
every thread in the root cgroup competes as if each is its own cgroup? ie.
Isn't the canonical solution here to create an enveloping group, at least
for share calculation purposes, for root threads and then assign them some
weight so that they compete in the same way that other cgroups do? Then, the
different modes go away or rather whatever the user wants can be expressed
via root's weight if that's to be made configurable.

Thanks.

-- 
tejun

Re: [PATCH v2 00/10] sched: Flatten the pick

[Peter Zijlstra]

On Mon, May 11, 2026 at 09:23:45AM -1000, Tejun Heo wrote:
> Hello, Peter.
> 
> On Mon, May 11, 2026 at 01:31:04PM +0200, Peter Zijlstra wrote:
> > So cgroup scheduling has always been a pain in the arse. The problems start
> > with weight distribution and end with hierachical picks and it all sucks.
> > 
> > The problems with weight distribution are related to that infernal global
> > fraction:
> > 
> >              tg->w * grq_i->w
> >    ge_i->w = ----------------
> >              \Sum_j grq_j->w
> > 
> > which we've approximated reasonably well by now. However, the immediate
> > consequence of this fraction is that the total group weight (tg->w) gets
> > fragmented across all your CPUs. And at 64 CPUs that means your per-cpu cgroup
> > weight ends up being a nice 19 task worth. And more CPUs more tiny. Combine
> > with the fact that 256 CPU systems are relatively common these days, this
> > becomes painful.
> > 
> > The common 'solution' is to inflate the group weight by 'nr_cpus'; the
> > immediate problem with that is that when all load of a group gets concentrated
> > on a single CPU, the per-cpu cgroup weight becomes insanely large, easily
> > exceeding nice -20.
> > 
> > Additionally there are numerical limits on the max weight you can have before
> > the math starts suffering overflows. As such there is a definite limit on the
> > total group weight. Which has annoyed people ;-)
> > 
> > The first few patches add a knob /debug/sched/cgroup_mode and a few different
> > options on how to deal with this. My favourite is 'concur', but obviously that
> > is also the most expensive one :-/ It adds a tg->tasks counter which makes the
> > update_tg_load_avg() thing more expensive.
> 
> Ignoring fixed math accuracy problems, isn't the root problem here that
> every thread in the root cgroup competes as if each is its own cgroup? ie.
> Isn't the canonical solution here to create an enveloping group, at least
> for share calculation purposes, for root threads and then assign them some
> weight so that they compete in the same way that other cgroups do? Then, the
> different modes go away or rather whatever the user wants can be expressed
> via root's weight if that's to be made configurable.

As long as the total group weight is a fraction; and it sorta has to be.
You can run into trouble by stacking that fraction.

Take 256 CPUs and a group weight of 1024. Then each CPU gets a weight of
1/256 or 4. Even if we increase the internal accuracy to 20 bits (we do
on 64bit) then this becomes 4096, do this for 2 more levels in the
hierarchy and you're down to scraping the barrel again.

So if each level runs at a fraction f of the level above, then level n
runs at f^n. Moving root into a phantom group at level 1, only solves
the problem against other tasks at level 1, but then you have the same
problem again at level 2 and below.

Both the numerical problems and the scale problem of the root group can
be avoided if we can get the average/nominal fraction to be near 1.

The 'normal' way around this is to ensure the group weight is nr_cpus *
1024, then, when everybody is running, the per CPU weight is 1024 or 1
and the continued fraction is also 1-ish. This is why people like to
increase the max group weight.

Trouble is of course that if not all CPUs are busy, with the extreme
being only a single CPU carrying that weight of nr_cpus*1024, this then
causes trouble because that one CPU gets overloaded.

One of the options is to simply put a max on the single CPU load; which
is the crudest option to just make it 'work'. The one I favour though is
the one where we scale the group weight by: 'min(cpumas, nr_tasks)'.

Anyway, this is why I've been looking at these alternative weight
schemes, to get the nominal fraction near 1 and make these problems go
away. It is both the numerical issues and the disparity between levels
(with root being at level 0 being the most obvious).


Does that make sense?

Re: [PATCH v2 00/10] sched: Flatten the pick

[Vincent Guittot]

On Mon, 11 May 2026 at 14:07, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Hi!
>
> So cgroup scheduling has always been a pain in the arse. The problems start
> with weight distribution and end with hierachical picks and it all sucks.
>
> The problems with weight distribution are related to that infernal global
> fraction:
>
>              tg->w * grq_i->w
>    ge_i->w = ----------------
>              \Sum_j grq_j->w
>
> which we've approximated reasonably well by now. However, the immediate
> consequence of this fraction is that the total group weight (tg->w) gets
> fragmented across all your CPUs. And at 64 CPUs that means your per-cpu cgroup
> weight ends up being a nice 19 task worth. And more CPUs more tiny. Combine
> with the fact that 256 CPU systems are relatively common these days, this
> becomes painful.
>
> The common 'solution' is to inflate the group weight by 'nr_cpus'; the
> immediate problem with that is that when all load of a group gets concentrated
> on a single CPU, the per-cpu cgroup weight becomes insanely large, easily
> exceeding nice -20.
>
> Additionally there are numerical limits on the max weight you can have before
> the math starts suffering overflows. As such there is a definite limit on the
> total group weight. Which has annoyed people ;-)
>
> The first few patches add a knob /debug/sched/cgroup_mode and a few different
> options on how to deal with this. My favourite is 'concur', but obviously that
> is also the most expensive one :-/ It adds a tg->tasks counter which makes the
> update_tg_load_avg() thing more expensive.
>
> I have some ideas but I figured I ought to share these things before sinking
> more time into it.
>
>
> On to the hierarchical pick; this has been causing trouble for a very long
> time. So once again an attempt at flatting it. The basic idea is to keep the
> full hierarchical load tracking as-is, but keep all the runnable entities in a
> single level. The immediate concequence of all this is ofcourse that we need to
> constantly re-compute the effective weight of each entity as things progress.
>
> Reweight is done on:
>  - enqueue
>  - pick -- or rather set_next_entity(.first=true)
>  - tick
>
> So while the {en,de}queue operations are still O(depth) due to the full
> accounting mess, the pick is now a single level. Removing the intermediate
> levels that obscure runnability etc.
>
>
> For testing, I've done a little experiment, I dug out what is colloqually known
> as a potato. A trusty old Sandybridge 12600k with a RX 580, and ran a game on
> it. From GOG, I had available 'Shadows: Awakens', a fun title that normally
> runs really well on this machine (provided you stick to 1080p).
>
> To make it interesting, I added 8 (one for each logical CPU) copies of: 'nice
> spin.sh'; this results in the game becoming almost unplayable, as in proper
> terrible.
>
> I used MangoHUD to record a few minutes of playtime for statistics, and then
> quit the came and re-started it with a shorter slice set (base/10). This
> results in the game being entirely playable -- not great, but definiltey
> playable.
>
>   Lutris / GE-Proton10-34 / Steam Runtime 3 (sniper)
>   Intel Core i7-2600K
>   AMD Radeon RX 580
>
>   Shadows Awakening (GOG)
>
>           default slice(*)
>
>   FPS min  3.8    20.6
>       avg 48.0    57.2
>       mag 87.4    80.3
>
>   FT  min   9.4    8.4
>       avg  34.5   19.5
>       max 107.4   37.2
>
>   FPS (Frames Per Second)
>   FT  (FrameTime)
>
>   [*] Command prefix: 'chrt -o --sched-runtime 280000 0'
>       effectively setting 'base_slice_ns/10'
>
> I have not compared to a kernel without flat on, just wanted to run non trivial
> workloads and play with slice to make sure everything 'works'.


I haven't reviewed the patches yet but I ran some tests with it while
testing sched latency related changes for short slice wakeup
preemption. I have some large hackbench regressions with this series
on HMP system with and without EAS. those figures are unexpected
because the benchs run on root cfs

One example with hackbench 8 groups thread pipe
tip/sched/core  tip/sched/core          +this patchset          +this patchset
slice 2.8ms     16ms                    2.8ms                   16ms
dragonboard rb5 with EAS
0,748(+/-4,6%)  0,621(+/-3.6%) +17%     1,915(+/-7.9%) -156%
0,689(+/- 9.1%) +8%

radxa orion6 HMP without EAS
0,588(+/-5.8%)  0,677(+/-5.9%) -15%     1,505(+/-10%) -156%
1,071(+/-5.9%) -82%

Increasing the slice partly removes regressions but tis is surprising
because the bench runs at root cfs and I thought that results will not
change in such a case

I will review the patchset and try to get what is going wrong


>
>
> Can also be had:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/flat
>
>  include/linux/cpuset.h |    6
>  include/linux/sched.h  |    1
>  kernel/cgroup/cpuset.c |   15
>  kernel/sched/core.c    |   47 --
>  kernel/sched/debug.c   |  171 +++++---
>  kernel/sched/fair.c    | 1038 ++++++++++++++++++++++---------------------------
>  kernel/sched/pelt.c    |    6
>  kernel/sched/sched.h   |   44 --
>  8 files changed, 672 insertions(+), 656 deletions(-)
>
> ---
> Change since v1 ( https://patch.msgid.link/20260317095113.387450089@infradead.org ):
>  - various Sashiko thingies
>  - rebase atop curren -tip
>
>

Re: [PATCH v2 00/10] sched: Flatten the pick

[Peter Zijlstra]

On Tue, May 12, 2026 at 10:42:33AM +0200, Vincent Guittot wrote:

> 
> I haven't reviewed the patches yet but I ran some tests with it while
> testing sched latency related changes for short slice wakeup
> preemption. I have some large hackbench regressions with this series
> on HMP system with and without EAS. those figures are unexpected
> because the benchs run on root cfs
> 
> One example with hackbench 8 groups thread pipe
> tip/sched/core  tip/sched/core          +this patchset          +this patchset
> slice 2.8ms     16ms                    2.8ms                   16ms
> dragonboard rb5 with EAS
> 0,748(+/-4,6%)  0,621(+/-3.6%) +17%     1,915(+/-7.9%) -156%
> 0,689(+/- 9.1%) +8%
> 
> radxa orion6 HMP without EAS
> 0,588(+/-5.8%)  0,677(+/-5.9%) -15%     1,505(+/-10%) -156%
> 1,071(+/-5.9%) -82%
> 
> Increasing the slice partly removes regressions but tis is surprising
> because the bench runs at root cfs and I thought that results will not
> change in such a case
> 
> I will review the patchset and try to get what is going wrong

Yeah, that is unexpected. Let me go have another look too.