From: Joel Fernandes <joel@joelfernandes.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
mingo@kernel.org, linux-kernel@vger.kernel.org,
juri.lelli@redhat.com, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, corbet@lwn.net, qyousef@layalina.io,
chris.hyser@oracle.com, patrick.bellasi@matbug.net,
pjt@google.com, pavel@ucw.cz, qperret@google.com,
tim.c.chen@linux.intel.com, joshdon@google.com, timj@gnu.org,
kprateek.nayak@amd.com, yu.c.chen@intel.com,
youssefesmat@chromium.org, efault@gmx.de
Subject: Re: [PATCH 14/17] sched/eevdf: Better handle mixed slice length
Date: Wed, 5 Apr 2023 16:05:55 -0400 [thread overview]
Message-ID: <CAEXW_YQmG83_Yb9JgXapt9RgAs4m=fHnrOKRqfG9N_VMYcA88A@mail.gmail.com> (raw)
In-Reply-To: <20230405083543.GZ4253@hirez.programming.kicks-ass.net>
On Wed, Apr 5, 2023 at 4:36 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Tue, Apr 04, 2023 at 01:50:50PM +0000, Joel Fernandes wrote:
> > On Tue, Apr 04, 2023 at 11:29:36AM +0200, Peter Zijlstra wrote:
>
> > > Heh, this is actually the correct behaviour. If you have a u=1 and a
> > > u=.5 task, you should distribute time on a 2:1 basis, eg. 67% vs 33%.
> >
> > Splitting like that sounds like starvation of the sleeper to me. If something
> > sleeps a lot, it will get even less CPU time on an average than it would if
> > there was no contention from the u=1 task.
>
> No, sleeping, per definition, means you're not contending for CPU. What
> CFS does, giving them a little boost, is strictly yuck and messes with
> latency -- because suddenly you have a task that said it wasn't
> competing appear as if it were, but you didn't run it (how could you, it
> wasn't there to run) -- but it still needs to catch up.
>
> The reason it does that, is mostly because at the time we didn't want to
> do the whole lag thing -- it's somewhat heavy on the u64 mults and 32bit
> computing was still a thing :/ So hacks happened.
Also you have the whole "boost tasks" that sleep a lot with CFS right?
Like a task handling user input sleeps a lot, but when it wakes up,
it gets higher dynamic priority as its vruntime did not advance. I
guess EEVDF also gets you the same thing but still messes with the CPU
usage?
> That said; I'm starting to regret not pushing the EEVDF thing harder
> back in 2010 when I first wrote it :/
>
> > And also CGroups will be even more weird than it already is in such a world,
> > 2 different containers will not get CPU time distributed properly- say if
> > tasks in one container sleep a lot and tasks in another container are CPU
> > bound.
>
> Cgroups are an abomination anyway :-) /me runs like hell. But no, I
> don't actually expect too much trouble there.
So, with 2 equally weighted containers, if one has a task that sleeps
50% of the time, and another has a 100% task, then the sleeper will
only run 33% of the time? I can see people running containers having a
problem with that (a customer running one container gets less CPU than
the other.). Sorry if I missed something.
But yeah I do find the whole EEVDF idea interesting but I admit I have
to research it more.
- Joel
next prev parent reply other threads:[~2023-04-05 20:06 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-28 9:26 [PATCH 00/17] sched: EEVDF using latency-nice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 01/17] sched: Introduce latency-nice as a per-task attribute Peter Zijlstra
2023-03-28 9:26 ` [PATCH 02/17] sched/fair: Add latency_offset Peter Zijlstra
2023-03-28 9:26 ` [PATCH 03/17] sched/fair: Add sched group latency support Peter Zijlstra
2023-03-28 9:26 ` [PATCH 04/17] sched/fair: Add avg_vruntime Peter Zijlstra
2023-03-28 23:57 ` Josh Don
2023-03-29 7:50 ` Peter Zijlstra
2023-04-05 19:13 ` Peter Zijlstra
2023-03-28 9:26 ` [PATCH 05/17] sched/fair: Remove START_DEBIT Peter Zijlstra
2023-03-28 9:26 ` [PATCH 06/17] sched/fair: Add lag based placement Peter Zijlstra
2023-04-03 9:18 ` Chen Yu
2023-04-05 9:47 ` Peter Zijlstra
2023-04-06 3:03 ` Chen Yu
2023-04-13 15:42 ` Chen Yu
2023-04-13 15:55 ` Chen Yu
2023-03-28 9:26 ` [PATCH 07/17] rbtree: Add rb_add_augmented_cached() helper Peter Zijlstra
2023-03-28 9:26 ` [PATCH 08/17] sched/fair: Implement an EEVDF like policy Peter Zijlstra
2023-03-29 1:26 ` Josh Don
2023-03-29 8:02 ` Peter Zijlstra
2023-03-29 8:06 ` Peter Zijlstra
2023-03-29 8:22 ` Peter Zijlstra
2023-03-29 18:48 ` Josh Don
2023-03-29 8:12 ` Peter Zijlstra
2023-03-29 18:54 ` Josh Don
2023-03-29 8:18 ` Peter Zijlstra
2023-03-29 14:35 ` Vincent Guittot
2023-03-30 8:01 ` Peter Zijlstra
2023-03-30 17:05 ` Vincent Guittot
2023-04-04 12:00 ` Peter Zijlstra
2023-03-28 9:26 ` [PATCH 09/17] sched: Commit to lag based placement Peter Zijlstra
2023-03-28 9:26 ` [PATCH 10/17] sched/smp: Use lag to simplify cross-runqueue placement Peter Zijlstra
2023-03-28 9:26 ` [PATCH 11/17] sched: Commit to EEVDF Peter Zijlstra
2023-03-28 9:26 ` [PATCH 12/17] sched/debug: Rename min_granularity to base_slice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 13/17] sched: Merge latency_offset into slice Peter Zijlstra
2023-03-28 9:26 ` [PATCH 14/17] sched/eevdf: Better handle mixed slice length Peter Zijlstra
2023-03-31 15:26 ` Vincent Guittot
2023-04-04 9:29 ` Peter Zijlstra
2023-04-04 13:50 ` Joel Fernandes
2023-04-05 5:41 ` Mike Galbraith
2023-04-05 8:35 ` Peter Zijlstra
2023-04-05 20:05 ` Joel Fernandes [this message]
2023-04-14 11:18 ` Phil Auld
2023-04-16 5:10 ` Joel Fernandes
[not found] ` <20230401232355.336-1-hdanton@sina.com>
2023-04-02 2:40 ` Mike Galbraith
2023-03-28 9:26 ` [PATCH 15/17] [RFC] sched/eevdf: Sleeper bonus Peter Zijlstra
2023-03-29 9:10 ` Mike Galbraith
2023-03-28 9:26 ` [PATCH 16/17] [RFC] sched/eevdf: Minimal vavg option Peter Zijlstra
2023-03-28 9:26 ` [PATCH 17/17] [DEBUG] sched/eevdf: Debug / validation crud Peter Zijlstra
2023-04-03 7:42 ` [PATCH 00/17] sched: EEVDF using latency-nice Shrikanth Hegde
2023-04-10 3:13 ` David Vernet
2023-04-11 2:09 ` David Vernet
[not found] ` <20230410082307.1327-1-hdanton@sina.com>
2023-04-11 10:15 ` Mike Galbraith
[not found] ` <20230411133333.1790-1-hdanton@sina.com>
2023-04-11 14:56 ` Mike Galbraith
[not found] ` <20230412025042.1413-1-hdanton@sina.com>
2023-04-12 4:05 ` Mike Galbraith
2023-04-25 12:32 ` Phil Auld
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='CAEXW_YQmG83_Yb9JgXapt9RgAs4m=fHnrOKRqfG9N_VMYcA88A@mail.gmail.com' \
--to=joel@joelfernandes.org \
--cc=bristot@redhat.com \
--cc=bsegall@google.com \
--cc=chris.hyser@oracle.com \
--cc=corbet@lwn.net \
--cc=dietmar.eggemann@arm.com \
--cc=efault@gmx.de \
--cc=joshdon@google.com \
--cc=juri.lelli@redhat.com \
--cc=kprateek.nayak@amd.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@suse.de \
--cc=mingo@kernel.org \
--cc=patrick.bellasi@matbug.net \
--cc=pavel@ucw.cz \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=qperret@google.com \
--cc=qyousef@layalina.io \
--cc=rostedt@goodmis.org \
--cc=tim.c.chen@linux.intel.com \
--cc=timj@gnu.org \
--cc=vincent.guittot@linaro.org \
--cc=youssefesmat@chromium.org \
--cc=yu.c.chen@intel.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).