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From: "Joel Fernandes (Google)" <>
Cc: "Joel Fernandes (Google)" <>,
	Dietmar Eggemann <>,
	Morten Ramussen <>,
	Ingo Molnar <>,
	Peter Zijlstra <>,
	Juri Lelli <>,
	Vincent Guittot <>,
	Patrick Bellasi <>,
	Rohit Jain <>,
Subject: [PATCH v2] sched: Remove obscure comment from select_task_rq_fair
Date: Sun, 27 May 2018 18:24:47 -0700	[thread overview]
Message-ID: <> (raw)

I was playing with cpusets and sched_load_balance flag and notice that
the fast-path (select_idle_sibling) can also be attempted for
exec-balance, not just wake-balance if the waker cpu's cpuset has
sched_load_balance = 0. This patch removes the obscure comment which was
saying this path can be entered only for wake-balance.

To trigger this, I just do:
mkdir /cpuset
mount -t cpuset none /cpuset
echo 0 > sched_load_balance

Then did some random activity and dumped the stack from 'if (!sd)' for
the non wake-balance cases.

Following is one of the stacks:

Turns out the same case occurs also during boot up when kthreadd tries
to create threads before domains are attached so lets fix the comment.

Cc: Dietmar Eggemann <>
Cc: Morten Ramussen <>
Cc: Ingo Molnar <>
Cc: Peter Zijlstra <>
Cc: Juri Lelli <>
Cc: Vincent Guittot <>
Cc: Patrick Bellasi <>
Cc: Rohit Jain <>
Signed-off-by: Joel Fernandes (Google) <>
v1->v2: Resending without "XXX" in subject since otherwise LKML thinks
its junk.

 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 54dc31e7ab9b..dd07794141d0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6665,7 +6665,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 	if (!sd) {
-		if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
+		if (sd_flag & SD_BALANCE_WAKE) {
 			new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
 			if (want_affine)

             reply	other threads:[~2018-05-28  1:24 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-28  1:24 Joel Fernandes (Google) [this message]
2018-05-28  7:15 ` Peter Zijlstra
2018-05-28 20:54   ` Joel Fernandes

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