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Date: Fri, 29 Apr 2022 20:36:00 -0000
From: "tip-bot2 for Dietmar Eggemann" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Dietmar Eggemann <dietmar.eggemann@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Refactor cpu_util_without()
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 4e3c7d338a2260406ae22eaf6d77b639d59bdc7e
Gitweb: https://git.kernel.org/tip/4e3c7d338a2260406ae22eaf6d77b639d59bdc7e
Author: Dietmar Eggemann <dietmar.eggemann@....com>
AuthorDate: Fri, 18 Mar 2022 17:36:56 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 29 Apr 2022 11:06:29 +02:00
sched/fair: Refactor cpu_util_without()
Except the 'task has no contribution or is new' condition at the
beginning of cpu_util_without(), which it shares with the load and
runnable counterpart functions, a cpu_util_next(..., dst_cpu = -1)
call can replace the rest of it.
The UTIL_EST specific check that task util_est has to be subtracted
from the CPU one in case of an enqueued (or current (to cater for the
wakeup - lb race)) task has to be moved to cpu_util_next().
This was initially introduced by commit c469933e7721
("sched/fair: Fix cpu_util_wake() for 'execl' type workloads").
UnixBench's `execl` throughput tests were run on the dual socket 40
CPUs Intel E5-2690 v2 to make sure it doesn't regress again.
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lore.kernel.org/r/20220318163656.954440-1-dietmar.eggemann@arm.com
---
kernel/sched/fair.c | 157 +++++++++++++++----------------------------
1 file changed, 57 insertions(+), 100 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4c42012..7d38728 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6544,108 +6544,19 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
}
/*
- * cpu_util_without: compute cpu utilization without any contributions from *p
- * @cpu: the CPU which utilization is requested
- * @p: the task which utilization should be discounted
- *
- * The utilization of a CPU is defined by the utilization of tasks currently
- * enqueued on that CPU as well as tasks which are currently sleeping after an
- * execution on that CPU.
- *
- * This method returns the utilization of the specified CPU by discounting the
- * utilization of the specified task, whenever the task is currently
- * contributing to the CPU utilization.
- */
-static unsigned long cpu_util_without(int cpu, struct task_struct *p)
-{
- struct cfs_rq *cfs_rq;
- unsigned int util;
-
- /* Task has no contribution or is new */
- if (cpu != task_cpu(p) || !READ_ONCE(p->se.avg.last_update_time))
- return cpu_util_cfs(cpu);
-
- cfs_rq = &cpu_rq(cpu)->cfs;
- util = READ_ONCE(cfs_rq->avg.util_avg);
-
- /* Discount task's util from CPU's util */
- lsub_positive(&util, task_util(p));
-
- /*
- * Covered cases:
- *
- * a) if *p is the only task sleeping on this CPU, then:
- * cpu_util (== task_util) > util_est (== 0)
- * and thus we return:
- * cpu_util_without = (cpu_util - task_util) = 0
- *
- * b) if other tasks are SLEEPING on this CPU, which is now exiting
- * IDLE, then:
- * cpu_util >= task_util
- * cpu_util > util_est (== 0)
- * and thus we discount *p's blocked utilization to return:
- * cpu_util_without = (cpu_util - task_util) >= 0
- *
- * c) if other tasks are RUNNABLE on that CPU and
- * util_est > cpu_util
- * then we use util_est since it returns a more restrictive
- * estimation of the spare capacity on that CPU, by just
- * considering the expected utilization of tasks already
- * runnable on that CPU.
- *
- * Cases a) and b) are covered by the above code, while case c) is
- * covered by the following code when estimated utilization is
- * enabled.
- */
- if (sched_feat(UTIL_EST)) {
- unsigned int estimated =
- READ_ONCE(cfs_rq->avg.util_est.enqueued);
-
- /*
- * Despite the following checks we still have a small window
- * for a possible race, when an execl's select_task_rq_fair()
- * races with LB's detach_task():
- *
- * detach_task()
- * p->on_rq = TASK_ON_RQ_MIGRATING;
- * ---------------------------------- A
- * deactivate_task() \
- * dequeue_task() + RaceTime
- * util_est_dequeue() /
- * ---------------------------------- B
- *
- * The additional check on "current == p" it's required to
- * properly fix the execl regression and it helps in further
- * reducing the chances for the above race.
- */
- if (unlikely(task_on_rq_queued(p) || current == p))
- lsub_positive(&estimated, _task_util_est(p));
-
- util = max(util, estimated);
- }
-
- /*
- * Utilization (estimated) can exceed the CPU capacity, thus let's
- * clamp to the maximum CPU capacity to ensure consistency with
- * cpu_util.
- */
- return min_t(unsigned long, util, capacity_orig_of(cpu));
-}
-
-/*
- * Predicts what cpu_util(@cpu) would return if @p was migrated (and enqueued)
- * to @dst_cpu.
+ * Predicts what cpu_util(@cpu) would return if @p was removed from @cpu
+ * (@dst_cpu = -1) or migrated to @dst_cpu.
*/
static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
{
struct cfs_rq *cfs_rq = &cpu_rq(cpu)->cfs;
- unsigned long util_est, util = READ_ONCE(cfs_rq->avg.util_avg);
+ unsigned long util = READ_ONCE(cfs_rq->avg.util_avg);
/*
- * If @p migrates from @cpu to another, remove its contribution. Or,
- * if @p migrates from another CPU to @cpu, add its contribution. In
- * the other cases, @cpu is not impacted by the migration, so the
- * util_avg should already be correct.
+ * If @dst_cpu is -1 or @p migrates from @cpu to @dst_cpu remove its
+ * contribution. If @p migrates from another CPU to @cpu add its
+ * contribution. In all the other cases @cpu is not impacted by the
+ * migration so its util_avg is already correct.
*/
if (task_cpu(p) == cpu && dst_cpu != cpu)
lsub_positive(&util, task_util(p));
@@ -6653,16 +6564,40 @@ static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
util += task_util(p);
if (sched_feat(UTIL_EST)) {
+ unsigned long util_est;
+
util_est = READ_ONCE(cfs_rq->avg.util_est.enqueued);
/*
- * During wake-up, the task isn't enqueued yet and doesn't
- * appear in the cfs_rq->avg.util_est.enqueued of any rq,
- * so just add it (if needed) to "simulate" what will be
- * cpu_util after the task has been enqueued.
+ * During wake-up @p isn't enqueued yet and doesn't contribute
+ * to any cpu_rq(cpu)->cfs.avg.util_est.enqueued.
+ * If @dst_cpu == @cpu add it to "simulate" cpu_util after @p
+ * has been enqueued.
+ *
+ * During exec (@dst_cpu = -1) @p is enqueued and does
+ * contribute to cpu_rq(cpu)->cfs.util_est.enqueued.
+ * Remove it to "simulate" cpu_util without @p's contribution.
+ *
+ * Despite the task_on_rq_queued(@p) check there is still a
+ * small window for a possible race when an exec
+ * select_task_rq_fair() races with LB's detach_task().
+ *
+ * detach_task()
+ * deactivate_task()
+ * p->on_rq = TASK_ON_RQ_MIGRATING;
+ * -------------------------------- A
+ * dequeue_task() \
+ * dequeue_task_fair() + Race Time
+ * util_est_dequeue() /
+ * -------------------------------- B
+ *
+ * The additional check "current == p" is required to further
+ * reduce the race window.
*/
if (dst_cpu == cpu)
util_est += _task_util_est(p);
+ else if (unlikely(task_on_rq_queued(p) || current == p))
+ lsub_positive(&util_est, _task_util_est(p));
util = max(util, util_est);
}
@@ -6671,6 +6606,28 @@ static unsigned long cpu_util_next(int cpu, struct task_struct *p, int dst_cpu)
}
/*
+ * cpu_util_without: compute cpu utilization without any contributions from *p
+ * @cpu: the CPU which utilization is requested
+ * @p: the task which utilization should be discounted
+ *
+ * The utilization of a CPU is defined by the utilization of tasks currently
+ * enqueued on that CPU as well as tasks which are currently sleeping after an
+ * execution on that CPU.
+ *
+ * This method returns the utilization of the specified CPU by discounting the
+ * utilization of the specified task, whenever the task is currently
+ * contributing to the CPU utilization.
+ */
+static unsigned long cpu_util_without(int cpu, struct task_struct *p)
+{
+ /* Task has no contribution or is new */
+ if (cpu != task_cpu(p) || !READ_ONCE(p->se.avg.last_update_time))
+ return cpu_util_cfs(cpu);
+
+ return cpu_util_next(cpu, p, -1);
+}
+
+/*
* compute_energy(): Estimates the energy that @pd would consume if @p was
* migrated to @dst_cpu. compute_energy() predicts what will be the utilization
* landscape of @pd's CPUs after the task migration, and uses the Energy Model
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