From: Josh Don <joshdon@google.com>
To: Abel Wu <wuyun.abel@bytedance.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Mel Gorman <mgorman@suse.de>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC v2 2/2] sched/fair: introduce sched-idle balance
Date: Wed, 13 Apr 2022 17:08:36 -0700 [thread overview]
Message-ID: <CABk29Nu9QTUKHP3cyx3qpiGcNM-PbaSxCvfhvBvOs++67KeXCw@mail.gmail.com> (raw)
In-Reply-To: <801da029-6bbe-2a0c-7de0-afffc3d5de02@bytedance.com>
> >> /*
> >> * Use locality-friendly rq->overloaded to cache the status of the rq
> >> * to minimize the heavy cost on LLC shared data.
> >> @@ -7837,6 +7867,22 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
> >> if (kthread_is_per_cpu(p))
> >> return 0;
> >>
> >> + if (unlikely(task_h_idle(p))) {
> >> + /*
> >> + * Disregard hierarchically idle tasks during sched-idle
> >> + * load balancing.
> >> + */
> >> + if (env->idle == CPU_SCHED_IDLE)
> >> + return 0;
> >> + } else if (!static_branch_unlikely(&sched_asym_cpucapacity)) {
> >> + /*
> >> + * It's not gonna help if stacking non-idle tasks on one
> >> + * cpu while leaving some idle.
> >> + */
> >> + if (cfs_rq_busy(env->src_rq) && !need_pull_cfs_task(env->dst_rq))
> >> + return 0;
> >
> > These checks don't involve the task at all, so this kind of check
> > should be pushed into the more general load balance function. But, I'm
> > not totally clear on the motivation here. If we have cpu A with 1
> > non-idle task and 100 idle tasks, and cpu B with 1 non-idle task, we
> > should definitely try to load balance some of the idle tasks from A to
> > B. idle tasks _do_ get time to run (although little), and this can add
> > up and cause antagonism to the non-idle task if there are a lot of
> > idle threads.
>
> CPU_SCHED_IDLE means triggered by sched_idle_balance() in which pulls
> a non-idle task for the unoccupied cpu from the overloaded ones, so
> idle tasks are not the target and should be skipped.
>
> The second part is: if we have cpu A with 1 non-idle task and 100 idle
> tasks, and B with >=1 non-idle task, we don't migrate the last non-idle
> task on A to B.
It could be possible that we do want to migrate the last non-idle task
from A to B, if the weight sum of idle tasks on A is very high (easily
possible with affinity restrictions). So I think we should leave
regular load balance alone here if it really wants to move the
non-idle task, and wrap this entire block in an if (env->idle ==
CPU_SCHED_IDLE).
Thanks,
Josh
next prev parent reply other threads:[~2022-04-14 0:08 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-09 13:51 [RFC v2 0/2] introduece sched-idle balance Abel Wu
2022-04-09 13:51 ` [RFC v2 1/2] sched/fair: filter out overloaded cpus in SIS Abel Wu
2022-04-12 1:23 ` Josh Don
2022-04-12 17:55 ` Abel Wu
2022-04-13 23:49 ` Josh Don
2022-04-14 15:36 ` Abel Wu
2022-04-15 23:21 ` Josh Don
2022-04-25 7:02 ` [sched/fair] 6b433275e3: stress-ng.sock.ops_per_sec 16.2% improvement kernel test robot
2022-04-09 13:51 ` [RFC v2 2/2] sched/fair: introduce sched-idle balance Abel Wu
2022-04-12 1:59 ` Josh Don
2022-04-12 17:56 ` Abel Wu
2022-04-14 0:08 ` Josh Don [this message]
2022-04-14 15:38 ` Abel Wu
2022-04-27 13:15 ` [sched/fair] ae44f2177f: reaim.jobs_per_min 2.3% improvement kernel test robot
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=CABk29Nu9QTUKHP3cyx3qpiGcNM-PbaSxCvfhvBvOs++67KeXCw@mail.gmail.com \
--to=joshdon@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=peterz@infradead.org \
--cc=vincent.guittot@linaro.org \
--cc=wuyun.abel@bytedance.com \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).