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sched/proxy: Optimize try_to_wake_up()

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The reason for the clause in try_to_wake_up() is, per its comment, that
find_proxy_task()'s proxy_deactivate() is not always called with a cleared
p->blocked_on.

However, that seems silly and easily cured. Make sure to always call
proxy_deactivate() with a cleared p->blocked_on such that we might remove this
clause from the common wake-up path.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260526113322.244729903%40infradead.org
This commit is contained in:
Peter Zijlstra
2026-05-26 11:28:46 +02:00
parent 1628b25248
commit abc40cca0e
1 changed files with 4 additions and 10 deletions
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14
kernel/sched/core.c
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@@ -4343,14 +4343,6 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
*/
WRITE_ONCE(p->__state, TASK_WAKING);
/*
* We never clear the blocked_on relation on proxy_deactivate.
* If we don't clear it here, we have TASK_RUNNING + p->blocked_on
* when waking up. Since this is a fully blocked, off CPU task
* waking up, it should be safe to clear the blocked_on relation.
*/
if (task_is_blocked(p))
clear_task_blocked_on(p, NULL);
/*
* If the owning (remote) CPU is still in the middle of schedule() with
* this task as prev, considering queueing p on the remote CPUs wake_list
@@ -6739,6 +6731,7 @@ static void proxy_deactivate(struct rq *rq, struct task_struct *donor)
unsigned long state = READ_ONCE(donor->__state);
WARN_ON_ONCE(state == TASK_RUNNING);
WARN_ON_ONCE(donor->blocked_on);
/*
* Because we got donor from pick_next_task(), it is *crucial*
* that we call proxy_resched_idle() before we deactivate it.
@@ -6864,9 +6857,9 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
for (p = donor; (mutex = p->blocked_on); p = owner) {
/* if its PROXY_WAKING, do return migration or run if current */
if (mutex == PROXY_WAKING) {
clear_task_blocked_on(p, PROXY_WAKING);
if (task_current(rq, p)) {
p->is_blocked = 0;
clear_task_blocked_on(p, PROXY_WAKING);
return p;
}
goto deactivate;
@@ -6900,9 +6893,9 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
* and return p (if it is current and safe to
* just run on this rq), or return-migrate the task.
*/
__clear_task_blocked_on(p, NULL);
if (task_current(rq, p)) {
p->is_blocked = 0;
__clear_task_blocked_on(p, NULL);
return p;
}
goto deactivate;
@@ -6912,6 +6905,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
/* XXX Don't handle blocked owners/delayed dequeue yet */
if (curr_in_chain)
return proxy_resched_idle(rq);
__clear_task_blocked_on(p, NULL);
goto deactivate;
}