[GIT PULL] scheduler fixes

Ingo Molnar
2017-03-07T20:33:32Z

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

# HEAD: f94c8d116997597fc00f0812b0ab9256e7b0c58f sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface

A fix for KVM's scheduler clock which (erroneously) was always marked unstable, a
fix for RT/DL load balancing, plus latency fixes.

Thanks,

Ingo

------------------>
Peter Zijlstra (3):
sched/fair: Make select_idle_cpu() more aggressive
sched/core: Fix pick_next_task() for RT,DL
sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface

arch/x86/kernel/cpu/amd.c | 4 ----
arch/x86/kernel/cpu/centaur.c | 2 --
arch/x86/kernel/cpu/common.c | 3 ---
arch/x86/kernel/cpu/cyrix.c | 1 -
arch/x86/kernel/cpu/intel.c | 4 ----
arch/x86/kernel/cpu/transmeta.c | 2 --
arch/x86/kernel/tsc.c | 35 +++++++++++++++++++++++------------
kernel/sched/core.c | 11 ++++++++---
kernel/sched/fair.c | 2 +-
kernel/sched/features.h | 5 +++++
10 files changed, 37 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4e95b2e0d95f..30d924ae5c34 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -555,10 +555,6 @@ static void early_init_amd(struct cpuinfo_x86 *c)
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
- if (check_tsc_unstable())
- clear_sched_clock_stable();
- } else {
- clear_sched_clock_stable();
}

/* Bit 12 of 8000_0007 edx is accumulated power mechanism. */
diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
index 2c234a6d94c4..bad8ff078a21 100644
--- a/arch/x86/kernel/cpu/centaur.c
+++ b/arch/x86/kernel/cpu/centaur.c
@@ -104,8 +104,6 @@ static void early_init_centaur(struct cpuinfo_x86 *c)
#ifdef CONFIG_X86_64
set_cpu_cap(c, X86_FEATURE_SYSENTER32);
#endif
-
- clear_sched_clock_stable();
}

static void init_centaur(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c64ca5929cb5..9d98e2e15d54 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -86,7 +86,6 @@ static void default_init(struct cpuinfo_x86 *c)
strcpy(c->x86_model_id, "386");
}
#endif
- clear_sched_clock_stable();
}

static const struct cpu_dev default_cpu = {
@@ -1075,8 +1074,6 @@ static void identify_cpu(struct cpuinfo_x86 *c)
*/
if (this_cpu->c_init)
this_cpu->c_init(c);
- else
- clear_sched_clock_stable();

/* Disable the PN if appropriate */
squash_the_stupid_serial_number(c);
diff --git a/arch/x86/kernel/cpu/cyrix.c b/arch/x86/kernel/cpu/cyrix.c
index 47416f959a48..31e679238e8d 100644
--- a/arch/x86/kernel/cpu/cyrix.c
+++ b/arch/x86/kernel/cpu/cyrix.c
@@ -184,7 +184,6 @@ static void early_init_cyrix(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_CYRIX_ARR);
break;
}
- clear_sched_clock_stable();
}

static void init_cyrix(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 017ecd3bb553..2388bafe5c37 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -161,10 +161,6 @@ static void early_init_intel(struct cpuinfo_x86 *c)
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
- if (check_tsc_unstable())
- clear_sched_clock_stable();
- } else {
- clear_sched_clock_stable();
}

/* Penwell and Cloverview have the TSC which doesn't sleep on S3 */
diff --git a/arch/x86/kernel/cpu/transmeta.c b/arch/x86/kernel/cpu/transmeta.c
index c1ea5b999839..6a9ad73a2c54 100644
--- a/arch/x86/kernel/cpu/transmeta.c
+++ b/arch/x86/kernel/cpu/transmeta.c
@@ -15,8 +15,6 @@ static void early_init_transmeta(struct cpuinfo_x86 *c)
if (xlvl >= 0x80860001)
c->x86_capability[CPUID_8086_0001_EDX] = cpuid_edx(0x80860001);
}
-
- clear_sched_clock_stable();
}

static void init_transmeta(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 2724dc82f992..911129fda2f9 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -326,9 +326,16 @@ unsigned long long sched_clock(void)
{
return paravirt_sched_clock();
}
+
+static inline bool using_native_sched_clock(void)
+{
+ return pv_time_ops.sched_clock == native_sched_clock;
+}
#else
unsigned long long
sched_clock(void) __attribute__((alias("native_sched_clock")));
+
+static inline bool using_native_sched_clock(void) { return true; }
#endif

int check_tsc_unstable(void)
@@ -1111,8 +1118,10 @@ static void tsc_cs_mark_unstable(struct clocksource *cs)
{
if (tsc_unstable)
return;
+
tsc_unstable = 1;
- clear_sched_clock_stable();
+ if (using_native_sched_clock())
+ clear_sched_clock_stable();
disable_sched_clock_irqtime();
pr_info("Marking TSC unstable due to clocksource watchdog\n");
}
@@ -1134,18 +1143,20 @@ static struct clocksource clocksource_tsc = {

void mark_tsc_unstable(char *reason)
{
- if (!tsc_unstable) {
- tsc_unstable = 1;
+ if (tsc_unstable)
+ return;
+
+ tsc_unstable = 1;
+ if (using_native_sched_clock())
clear_sched_clock_stable();
- disable_sched_clock_irqtime();
- pr_info("Marking TSC unstable due to %s\n", reason);
- /* Change only the rating, when not registered */
- if (clocksource_tsc.mult)
- clocksource_mark_unstable(&clocksource_tsc);
- else {
- clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE;
- clocksource_tsc.rating = 0;
- }
+ disable_sched_clock_irqtime();
+ pr_info("Marking TSC unstable due to %s\n", reason);
+ /* Change only the rating, when not registered */
+ if (clocksource_tsc.mult) {
+ clocksource_mark_unstable(&clocksource_tsc);
+ } else {
+ clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE;
+ clocksource_tsc.rating = 0;
}
}

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bbfb917a9b49..6699d43a8843 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3273,10 +3273,15 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *p;

/*
- * Optimization: we know that if all tasks are in
- * the fair class we can call that function directly:
+ * Optimization: we know that if all tasks are in the fair class we can
+ * call that function directly, but only if the @prev task wasn't of a
+ * higher scheduling class, because otherwise those loose the
+ * opportunity to pull in more work from other CPUs.
*/
- if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
+ if (likely((prev->sched_class == &idle_sched_class ||
+ prev->sched_class == &fair_sched_class) &&
+ rq->nr_running == rq->cfs.h_nr_running)) {
+
p = fair_sched_class.pick_next_task(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
goto again;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 274c747a01ce..b3ee10dd3e85 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5797,7 +5797,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
* Due to large variance we need a large fuzz factor; hackbench in
* particularly is sensitive here.
*/
- if ((avg_idle / 512) < avg_cost)
+ if (sched_feat(SIS_AVG_CPU) && (avg_idle / 512) < avg_cost)
return -1;

time = local_clock();
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 69631fa46c2f..1b3c8189b286 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -51,6 +51,11 @@ SCHED_FEAT(NONTASK_CAPACITY, true)
*/
SCHED_FEAT(TTWU_QUEUE, true)

+/*
+ * When doing wakeups, attempt to limit superfluous scans of the LLC domain.
+ */
+SCHED_FEAT(SIS_AVG_CPU, false)
+
#ifdef HAVE_RT_PUSH_IPI
/*
* In order to avoid a thundering herd attack of CPUs that are