From: tip-bot for Vincent Guittot <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: peterz@infradead.org, linux-kernel@vger.kernel.org,
torvalds@linux-foundation.org, hpa@zytor.com,
vincent.guittot@linaro.org, tglx@linutronix.de, mingo@kernel.org
Subject: [tip:sched/core] sched/fair: Fix imbalance due to CPU affinity
Date: Thu, 25 Jul 2019 09:13:52 -0700 [thread overview]
Message-ID: <tip-f6cad8df6b30a5d2bbbd2e698f74b4cafb9fb82b@git.kernel.org> (raw)
In-Reply-To: <1561996022-28829-1-git-send-email-vincent.guittot@linaro.org>
Commit-ID: f6cad8df6b30a5d2bbbd2e698f74b4cafb9fb82b
Gitweb: https://git.kernel.org/tip/f6cad8df6b30a5d2bbbd2e698f74b4cafb9fb82b
Author: Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate: Mon, 1 Jul 2019 17:47:02 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 25 Jul 2019 15:51:52 +0200
sched/fair: Fix imbalance due to CPU affinity
The load_balance() has a dedicated mecanism to detect when an imbalance
is due to CPU affinity and must be handled at parent level. In this case,
the imbalance field of the parent's sched_group is set.
The description of sg_imbalanced() gives a typical example of two groups
of 4 CPUs each and 4 tasks each with a cpumask covering 1 CPU of the first
group and 3 CPUs of the second group. Something like:
{ 0 1 2 3 } { 4 5 6 7 }
* * * *
But the load_balance fails to fix this UC on my octo cores system
made of 2 clusters of quad cores.
Whereas the load_balance is able to detect that the imbalanced is due to
CPU affinity, it fails to fix it because the imbalance field is cleared
before letting parent level a chance to run. In fact, when the imbalance is
detected, the load_balance reruns without the CPU with pinned tasks. But
there is no other running tasks in the situation described above and
everything looks balanced this time so the imbalance field is immediately
cleared.
The imbalance field should not be cleared if there is no other task to move
when the imbalance is detected.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1561996022-28829-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b5546a15206c..9be36ffb5689 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9048,9 +9048,10 @@ more_balance:
out_balanced:
/*
* We reach balance although we may have faced some affinity
- * constraints. Clear the imbalance flag if it was set.
+ * constraints. Clear the imbalance flag only if other tasks got
+ * a chance to move and fix the imbalance.
*/
- if (sd_parent) {
+ if (sd_parent && !(env.flags & LBF_ALL_PINNED)) {
int *group_imbalance = &sd_parent->groups->sgc->imbalance;
if (*group_imbalance)
prev parent reply other threads:[~2019-07-25 16:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-01 15:47 [PATCH v2] sched/fair: fix imbalance due to CPU affinity Vincent Guittot
2019-07-01 19:03 ` Peter Zijlstra
2019-07-02 9:34 ` Valentin Schneider
2019-07-02 10:00 ` Vincent Guittot
2019-07-02 14:29 ` Valentin Schneider
2019-07-05 12:23 ` Vincent Guittot
2019-07-25 16:13 ` tip-bot for Vincent Guittot [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=tip-f6cad8df6b30a5d2bbbd2e698f74b4cafb9fb82b@git.kernel.org \
--to=tipbot@zytor.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tip-commits@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.