[tip:,sched/core] sched/core: Reduce cost of sched_move_task when config autogroup
Commit Message
The following commit has been merged into the sched/core branch of tip:
Commit-ID: eff6c8ce8d4d7faef75f66614dd20bb50595d261
Gitweb: https://git.kernel.org/tip/eff6c8ce8d4d7faef75f66614dd20bb50595d261
Author: wuchi <wuchi.zero@gmail.com>
AuthorDate: Tue, 21 Mar 2023 14:44:59 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 22 Mar 2023 10:10:58 +01:00
sched/core: Reduce cost of sched_move_task when config autogroup
Some sched_move_task calls are useless because that
task_struct->sched_task_group maybe not changed (equals task_group
of cpu_cgroup) when system enable autogroup. So do some checks in
sched_move_task.
sched_move_task eg:
task A belongs to cpu_cgroup0 and autogroup0, it will always belong
to cpu_cgroup0 when do_exit. So there is no need to do {de|en}queue.
The call graph is as follow.
do_exit
sched_autogroup_exit_task
sched_move_task
dequeue_task
sched_change_group
A.sched_task_group = sched_get_task_group (=cpu_cgroup0)
enqueue_task
Performance results:
===========================
1. env
cpu: bogomips=4600.00
kernel: 6.3.0-rc3
cpu_cgroup: 6:cpu,cpuacct:/user.slice
2. cmds
do_exit script:
for i in {0..10000}; do
sleep 0 &
done
wait
Run the above script, then use the following bpftrace cmd to get
the cost of sched_move_task:
bpftrace -e 'k:sched_move_task { @ts[tid] = nsecs; }
kr:sched_move_task /@ts[tid]/
{ @ns += nsecs - @ts[tid]; delete(@ts[tid]); }'
3. cost time(ns):
without patch: 43528033
with patch: 18541416
diff:-24986617 -57.4%
As the result show, the patch will save 57.4% in the scenario.
Signed-off-by: wuchi <wuchi.zero@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230321064459.39421-1-wuchi.zero@gmail.com
---
kernel/sched/core.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
@@ -10351,7 +10351,7 @@ void sched_release_group(struct task_group *tg)
spin_unlock_irqrestore(&task_group_lock, flags);
}
-static void sched_change_group(struct task_struct *tsk)
+static struct task_group *sched_get_task_group(struct task_struct *tsk)
{
struct task_group *tg;
@@ -10363,7 +10363,13 @@ static void sched_change_group(struct task_struct *tsk)
tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
struct task_group, css);
tg = autogroup_task_group(tsk, tg);
- tsk->sched_task_group = tg;
+
+ return tg;
+}
+
+static void sched_change_group(struct task_struct *tsk, struct task_group *group)
+{
+ tsk->sched_task_group = group;
#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->task_change_group)
@@ -10384,10 +10390,19 @@ void sched_move_task(struct task_struct *tsk)
{
int queued, running, queue_flags =
DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
+ struct task_group *group;
struct rq_flags rf;
struct rq *rq;
rq = task_rq_lock(tsk, &rf);
+ /*
+ * Esp. with SCHED_AUTOGROUP enabled it is possible to get superfluous
+ * group changes.
+ */
+ group = sched_get_task_group(tsk);
+ if (group == tsk->sched_task_group)
+ goto unlock;
+
update_rq_clock(rq);
running = task_current(rq, tsk);
@@ -10398,7 +10413,7 @@ void sched_move_task(struct task_struct *tsk)
if (running)
put_prev_task(rq, tsk);
- sched_change_group(tsk);
+ sched_change_group(tsk, group);
if (queued)
enqueue_task(rq, tsk, queue_flags);
@@ -10412,6 +10427,7 @@ void sched_move_task(struct task_struct *tsk)
resched_curr(rq);
}
+unlock:
task_rq_unlock(rq, tsk, &rf);
}