sched/core: Skip rq->avg_idle update without a valid idle_stamp

Browse source

Commit 4b603f1551 ("sched: Update rq->avg_idle when a task is moved
to an idle CPU") moved rq->avg_idle accounting out of the wakeup path and
into put_prev_task_idle(), so that the idle interval is consumed whenever
the idle task is switched out.

The wakeup-side accounting that it replaced only updated rq->avg_idle
when rq->idle_stamp was non-zero. The new helper lost that validity
check and unconditionally computes:

	rq_clock(rq) - rq->idle_stamp

If rq->idle_stamp is zero, this uses rq_clock(rq) as the sample. That is
not a valid idle duration and can immediately drive rq->avg_idle to its
clamp.

This can happen when sched_balance_newidle() returns before setting
rq->idle_stamp, for example when this_rq->ttwu_pending is set. In that
case the rq can switch to the idle task with idle_stamp still zero and
leave idle again when the pending wakeup is processed.

Other paths can also switch to the idle task without setting
rq->idle_stamp via newidle_balance(), for example find_proxy_task() or
force-idling.

Restore the idle_stamp validity check in update_rq_avg_idle() and skip
the rq->avg_idle update when there is no measured idle interval.

Fixes: 4b603f1551 ("sched: Update rq->avg_idle when a task is moved to an idle CPU")
Signed-off-by: Shubhang Kaushik (Ampere) <sh@gentwo.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260807-master-v3-1-c328354efed3@gentwo.org

...

This commit is contained in:

Shubhang Kaushik (Ampere) 2026-08-07 13:38:52 -07:00 • committed by Peter Zijlstra

parent dae5c02920

commit c6dcd97c8b

1 changed files with 8 additions and 2 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

10

kernel/sched/core.c

View file