[GIT PULL] scheduler fixes

Ingo Molnar
2011-12-05T18:51:24Z

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

Thanks,

Ingo

------------------>
Carsten Emde (1):
sched: Set the command name of the idle tasks in SMP kernels

Hui Kang (1):
sched_fair: Fix a typo in the comment describing update_sd_lb_stats

J. Bruce Fields (1):
sched: Document wait_for_completion_*() return values

Paul Turner (1):
sched: Fix buglet in return_cfs_rq_runtime()

Peter Zijlstra (3):
sched: Add a comment to effective_load() since it's a pain
sched, rt: Provide means of disabling cross-cpu bandwidth sharing
sched: Avoid SMT siblings in select_idle_sibling() if possible

Salman Qazi (1):
sched, x86: Avoid unnecessary overflow in sched_clock

arch/x86/include/asm/timer.h | 23 ++++++-
include/linux/init_task.h | 4 +-
kernel/sched.c | 17 +++++
kernel/sched_fair.c | 159 +++++++++++++++++++++++++++++++++---------
kernel/sched_features.h | 1 +
kernel/sched_rt.c | 3 +
6 files changed, 171 insertions(+), 36 deletions(-)

diff --git a/arch/x86/include/asm/timer.h b/arch/x86/include/asm/timer.h
index fa7b917..431793e 100644
--- a/arch/x86/include/asm/timer.h
+++ b/arch/x86/include/asm/timer.h
@@ -32,6 +32,22 @@ extern int no_timer_check;
* (mathieu.desnoyers@polymtl.ca)
*
* -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ *
+ * In:
+ *
+ * ns = cycles * cyc2ns_scale / SC
+ *
+ * Although we may still have enough bits to store the value of ns,
+ * in some cases, we may not have enough bits to store cycles * cyc2ns_scale,
+ * leading to an incorrect result.
+ *
+ * To avoid this, we can decompose 'cycles' into quotient and remainder
+ * of division by SC. Then,
+ *
+ * ns = (quot * SC + rem) * cyc2ns_scale / SC
+ * = quot * cyc2ns_scale + (rem * cyc2ns_scale) / SC
+ *
+ * - sqazi@google.com
*/

DECLARE_PER_CPU(unsigned long, cyc2ns);
@@ -41,9 +57,14 @@ DECLARE_PER_CPU(unsigned long long, cyc2ns_offset);

static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
+ unsigned long long quot;
+ unsigned long long rem;
int cpu = smp_processor_id();
unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
- ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR;
+ quot = (cyc >> CYC2NS_SCALE_FACTOR);
+ rem = cyc & ((1ULL << CYC2NS_SCALE_FACTOR) - 1);
+ ns += quot * per_cpu(cyc2ns, cpu) +
+ ((rem * per_cpu(cyc2ns, cpu)) >> CYC2NS_SCALE_FACTOR);
return ns;
}

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 08ffab0..b6e5b8b 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -126,6 +126,8 @@ extern struct cred init_cred;
# define INIT_PERF_EVENTS(tsk)
#endif

+#define INIT_TASK_COMM "swapper"
+
/*
* INIT_TASK is used to set up the first task table, touch at
* your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -162,7 +164,7 @@ extern struct cred init_cred;
.group_leader = &tsk, \
RCU_INIT_POINTER(.real_cred, &init_cred), \
RCU_INIT_POINTER(.cred, &init_cred), \
- .comm = "swapper", \
+ .comm = INIT_TASK_COMM, \
.thread = INIT_THREAD, \
.fs = &init_fs, \
.files = &init_files, \
diff --git a/kernel/sched.c b/kernel/sched.c
index 0e9344a..d6b149c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -71,6 +71,7 @@
#include <linux/ctype.h>
#include <linux/ftrace.h>
#include <linux/slab.h>
+#include <linux/init_task.h>

#include <asm/tlb.h>
#include <asm/irq_regs.h>
@@ -4810,6 +4811,9 @@ EXPORT_SYMBOL(wait_for_completion);
* This waits for either a completion of a specific task to be signaled or for a
* specified timeout to expire. The timeout is in jiffies. It is not
* interruptible.
+ *
+ * The return value is 0 if timed out, and positive (at least 1, or number of
+ * jiffies left till timeout) if completed.
*/
unsigned long __sched
wait_for_completion_timeout(struct completion *x, unsigned long timeout)
@@ -4824,6 +4828,8 @@ EXPORT_SYMBOL(wait_for_completion_timeout);
*
* This waits for completion of a specific task to be signaled. It is
* interruptible.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if completed.
*/
int __sched wait_for_completion_interruptible(struct completion *x)
{
@@ -4841,6 +4847,9 @@ EXPORT_SYMBOL(wait_for_completion_interruptible);
*
* This waits for either a completion of a specific task to be signaled or for a
* specified timeout to expire. It is interruptible. The timeout is in jiffies.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if timed out,
+ * positive (at least 1, or number of jiffies left till timeout) if completed.
*/
long __sched
wait_for_completion_interruptible_timeout(struct completion *x,
@@ -4856,6 +4865,8 @@ EXPORT_SYMBOL(wait_for_completion_interruptible_timeout);
*
* This waits to be signaled for completion of a specific task. It can be
* interrupted by a kill signal.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if completed.
*/
int __sched wait_for_completion_killable(struct completion *x)
{
@@ -4874,6 +4885,9 @@ EXPORT_SYMBOL(wait_for_completion_killable);
* This waits for either a completion of a specific task to be
* signaled or for a specified timeout to expire. It can be
* interrupted by a kill signal. The timeout is in jiffies.
+ *
+ * The return value is -ERESTARTSYS if interrupted, 0 if timed out,
+ * positive (at least 1, or number of jiffies left till timeout) if completed.
*/
long __sched
wait_for_completion_killable_timeout(struct completion *x,
@@ -6099,6 +6113,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
*/
idle->sched_class = &idle_sched_class;
ftrace_graph_init_idle_task(idle, cpu);
+#if defined(CONFIG_SMP)
+ sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
+#endif
}

/*
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 5c9e679..a78ed27 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -772,19 +772,32 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
list_del_leaf_cfs_rq(cfs_rq);
}

+static inline long calc_tg_weight(struct task_group *tg, struct cfs_rq *cfs_rq)
+{
+ long tg_weight;
+
+ /*
+ * Use this CPU's actual weight instead of the last load_contribution
+ * to gain a more accurate current total weight. See
+ * update_cfs_rq_load_contribution().
+ */
+ tg_weight = atomic_read(&tg->load_weight);
+ tg_weight -= cfs_rq->load_contribution;
+ tg_weight += cfs_rq->load.weight;
+
+ return tg_weight;
+}
+
static long calc_cfs_shares(struct cfs_rq *cfs_rq, struct task_group *tg)
{
- long load_weight, load, shares;
+ long tg_weight, load, shares;

+ tg_weight = calc_tg_weight(tg, cfs_rq);
load = cfs_rq->load.weight;

- load_weight = atomic_read(&tg->load_weight);
- load_weight += load;
- load_weight -= cfs_rq->load_contribution;
-
shares = (tg->shares * load);
- if (load_weight)
- shares /= load_weight;
+ if (tg_weight)
+ shares /= tg_weight;

if (shares < MIN_SHARES)
shares = MIN_SHARES;
@@ -1743,7 +1756,7 @@ static void __return_cfs_rq_runtime(struct cfs_rq *cfs_rq)

static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
{
- if (!cfs_rq->runtime_enabled || !cfs_rq->nr_running)
+ if (!cfs_rq->runtime_enabled || cfs_rq->nr_running)
return;

__return_cfs_rq_runtime(cfs_rq);
@@ -2036,36 +2049,100 @@ static void task_waking_fair(struct task_struct *p)
* Adding load to a group doesn't make a group heavier, but can cause movement
* of group shares between cpus. Assuming the shares were perfectly aligned one
* can calculate the shift in shares.
+ *
+ * Calculate the effective load difference if @wl is added (subtracted) to @tg
+ * on this @cpu and results in a total addition (subtraction) of @wg to the
+ * total group weight.
+ *
+ * Given a runqueue weight distribution (rw_i) we can compute a shares
+ * distribution (s_i) using:
+ *
+ * s_i = rw_i / \Sum rw_j (1)
+ *
+ * Suppose we have 4 CPUs and our @tg is a direct child of the root group and
+ * has 7 equal weight tasks, distributed as below (rw_i), with the resulting
+ * shares distribution (s_i):
+ *
+ * rw_i = { 2, 4, 1, 0 }
+ * s_i = { 2/7, 4/7, 1/7, 0 }
+ *
+ * As per wake_affine() we're interested in the load of two CPUs (the CPU the
+ * task used to run on and the CPU the waker is running on), we need to
+ * compute the effect of waking a task on either CPU and, in case of a sync
+ * wakeup, compute the effect of the current task going to sleep.
+ *
+ * So for a change of @wl to the local @cpu with an overall group weight change
+ * of @wl we can compute the new shares distribution (s'_i) using:
+ *
+ * s'_i = (rw_i + @wl) / (@wg + \Sum rw_j) (2)
+ *
+ * Suppose we're interested in CPUs 0 and 1, and want to compute the load
+ * differences in waking a task to CPU 0. The additional task changes the
+ * weight and shares distributions like:
+ *
+ * rw'_i = { 3, 4, 1, 0 }
+ * s'_i = { 3/8, 4/8, 1/8, 0 }
+ *
+ * We can then compute the difference in effective weight by using:
+ *
+ * dw_i = S * (s'_i - s_i) (3)
+ *
+ * Where 'S' is the group weight as seen by its parent.
+ *
+ * Therefore the effective change in loads on CPU 0 would be 5/56 (3/8 - 2/7)
+ * times the weight of the group. The effect on CPU 1 would be -4/56 (4/8 -
+ * 4/7) times the weight of the group.
*/
static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
{
struct sched_entity *se = tg->se[cpu];

- if (!tg->parent)
+ if (!tg->parent) /* the trivial, non-cgroup case */
return wl;

for_each_sched_entity(se) {
- long lw, w;
+ long w, W;

tg = se->my_q->tg;
- w = se->my_q->load.weight;

- /* use this cpu's instantaneous contribution */
- lw = atomic_read(&tg->load_weight);
- lw -= se->my_q->load_contribution;
- lw += w + wg;
+ /*
+ * W = @wg + \Sum rw_j
+ */
+ W = wg + calc_tg_weight(tg, se->my_q);

- wl += w;
+ /*
+ * w = rw_i + @wl
+ */
+ w = se->my_q->load.weight + wl;

- if (lw > 0 && wl < lw)
- wl = (wl * tg->shares) / lw;
+ /*
+ * wl = S * s'_i; see (2)
+ */
+ if (W > 0 && w < W)
+ wl = (w * tg->shares) / W;
else
wl = tg->shares;

- /* zero point is MIN_SHARES */
+ /*
+ * Per the above, wl is the new se->load.weight value; since
+ * those are clipped to [MIN_SHARES, ...) do so now. See
+ * calc_cfs_shares().
+ */
if (wl < MIN_SHARES)
wl = MIN_SHARES;
+
+ /*
+ * wl = dw_i = S * (s'_i - s_i); see (3)
+ */
wl -= se->load.weight;
+
+ /*
+ * Recursively apply this logic to all parent groups to compute
+ * the final effective load change on the root group. Since
+ * only the @tg group gets extra weight, all parent groups can
+ * only redistribute existing shares. @wl is the shift in shares
+ * resulting from this level per the above.
+ */
wg = 0;
}

@@ -2249,7 +2326,8 @@ static int select_idle_sibling(struct task_struct *p, int target)
int cpu = smp_processor_id();
int prev_cpu = task_cpu(p);
struct sched_domain *sd;
- int i;
+ struct sched_group *sg;
+ int i, smt = 0;

/*
* If the task is going to be woken-up on this cpu and if it is
@@ -2269,25 +2347,38 @@ static int select_idle_sibling(struct task_struct *p, int target)
* Otherwise, iterate the domains and find an elegible idle cpu.
*/
rcu_read_lock();
+again:
for_each_domain(target, sd) {
- if (!(sd->flags & SD_SHARE_PKG_RESOURCES))
- break;
+ if (!smt && (sd->flags & SD_SHARE_CPUPOWER))
+ continue;

- for_each_cpu_and(i, sched_domain_span(sd), tsk_cpus_allowed(p)) {
- if (idle_cpu(i)) {
- target = i;
- break;
+ if (!(sd->flags & SD_SHARE_PKG_RESOURCES)) {
+ if (!smt) {
+ smt = 1;
+ goto again;
}
+ break;
}

- /*
- * Lets stop looking for an idle sibling when we reached
- * the domain that spans the current cpu and prev_cpu.
- */
- if (cpumask_test_cpu(cpu, sched_domain_span(sd)) &&
- cpumask_test_cpu(prev_cpu, sched_domain_span(sd)))
- break;
+ sg = sd->groups;
+ do {
+ if (!cpumask_intersects(sched_group_cpus(sg),
+ tsk_cpus_allowed(p)))
+ goto next;
+
+ for_each_cpu(i, sched_group_cpus(sg)) {
+ if (!idle_cpu(i))
+ goto next;
+ }
+
+ target = cpumask_first_and(sched_group_cpus(sg),
+ tsk_cpus_allowed(p));
+ goto done;
+next:
+ sg = sg->next;
+ } while (sg != sd->groups);
}
+done:
rcu_read_unlock();

return target;
@@ -3511,7 +3602,7 @@ static bool update_sd_pick_busiest(struct sched_domain *sd,
}

/**
- * update_sd_lb_stats - Update sched_group's statistics for load balancing.
+ * update_sd_lb_stats - Update sched_domain's statistics for load balancing.
* @sd: sched_domain whose statistics are to be updated.
* @this_cpu: Cpu for which load balance is currently performed.
* @idle: Idle status of this_cpu
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index efa0a7b..8480224 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -67,3 +67,4 @@ SCHED_FEAT(NONTASK_POWER, 1)
SCHED_FEAT(TTWU_QUEUE, 1)

SCHED_FEAT(FORCE_SD_OVERLAP, 0)
+SCHED_FEAT(RT_RUNTIME_SHARE, 1)
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 056cbd2..583a136 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -560,6 +560,9 @@ static int balance_runtime(struct rt_rq *rt_rq)
{
int more = 0;

+ if (!sched_feat(RT_RUNTIME_SHARE))
+ return more;
+
if (rt_rq->rt_time > rt_rq->rt_runtime) {
raw_spin_unlock(&rt_rq->rt_runtime_lock);
more = do_balance_runtime(rt_rq);