From: Abel Wu <wuyun.abel@bytedance.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ben Segall <bsegall@google.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>, Mel Gorman <mgorman@suse.de>,
Steven Rostedt <rostedt@goodmis.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/5] introduce sched-idle balancing
Date: Fri, 25 Feb 2022 14:46:15 +0800 [thread overview]
Message-ID: <9fe00f72-4e2e-38ff-d64a-4ae41e683316@bytedance.com> (raw)
In-Reply-To: <YheiT2pGNDggdFSu@hirez.programming.kicks-ass.net>
Hi Peter,
On 2/24/22 11:20 PM, Peter Zijlstra Wrote:
> On Thu, Feb 17, 2022 at 11:43:56PM +0800, Abel Wu wrote:
>> Current load balancing is mainly based on cpu capacity
>> and task util, which makes sense in the POV of overall
>> throughput. While there still might be some improvement
>> can be done by reducing number of overloaded cfs rqs if
>> sched-idle or idle rq exists.
>
> I'm much confused, there is an explicit new-idle balancer and a periodic
> idle balancer already there.
The two balancers are triggered on the rqs that have no tasks on them,
and load_balance() seems don't show a preference for non-idle tasks so
there might be possibility that only idle tasks are pulled during load
balance while overloaded rqs (rq->cfs.h_nr_running > 1) exist. As a
result the normal tasks, mostly latency-critical ones in our case, on
that overloaded rq still suffer waiting for each other. I observed this
through perf sched.
IOW the main difference from the POV of load_balance() between the
latency-critical tasks and the idle ones is load.
The sched-idle balancer is triggered on the sched-idle rqs periodically
and the newly-idle ones. It does a 'fast' pull of non-idle tasks from
the overloaded rqs to the sched-idle/idle ones to let the non-idle tasks
make full use of cpu resources.
The sched-idle balancer only focuses on non-idle tasks' performance, so
it can introduce overall load imbalance, and that's why I put it before
load_balance().
Best Regards,
Abel
next prev parent reply other threads:[~2022-02-25 6:46 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-17 15:43 [RFC PATCH 0/5] introduce sched-idle balancing Abel Wu
2022-02-17 15:43 ` [RFC PATCH 1/5] sched/fair: record overloaded cpus Abel Wu
2022-02-24 7:10 ` Gautham R. Shenoy
2022-02-24 14:36 ` Abel Wu
2022-02-27 8:08 ` Aubrey Li
2022-02-17 15:43 ` [RFC PATCH 2/5] sched/fair: introduce sched-idle balance Abel Wu
2022-02-17 15:43 ` [RFC PATCH 3/5] sched/fair: add stats for sched-idle balancing Abel Wu
2022-02-17 15:44 ` [RFC PATCH 4/5] sched/fair: filter out overloaded cpus in sis Abel Wu
2022-02-17 15:44 ` [RFC PATCH 5/5] sched/fair: favor cpu capacity for idle tasks Abel Wu
2022-02-24 3:19 ` [RFC PATCH 0/5] introduce sched-idle balancing Abel Wu
2022-02-24 15:20 ` Peter Zijlstra
2022-02-24 15:29 ` Vincent Guittot
2022-02-25 6:51 ` Abel Wu
2022-02-25 6:46 ` Abel Wu [this message]
2022-02-25 8:29 ` Vincent Guittot
2022-02-25 10:46 ` Abel Wu
2022-02-25 13:15 ` Vincent Guittot
2022-02-24 16:47 ` Mel Gorman
2022-02-25 8:15 ` Abel Wu
2022-02-25 10:16 ` Mel Gorman
2022-02-25 13:20 ` Abel Wu
2022-03-02 0:41 ` Josh Don
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=9fe00f72-4e2e-38ff-d64a-4ae41e683316@bytedance.com \
--to=wuyun.abel@bytedance.com \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.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 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).