From: Vincent Guittot <vincent.guittot@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
Yuyang Du <yuyang.du@intel.com>, Paul Turner <pjt@google.com>,
Ben Segall <bsegall@google.com>
Subject: Re: [PATCH v2] sched/fair: update scale invariance of PELT
Date: Thu, 13 Apr 2017 17:16:20 +0200 [thread overview]
Message-ID: <CAKfTPtANR173Hr1K4TOR1DbD6N6qty8V0eTgbKmVmfQUxkJ0Zw@mail.gmail.com> (raw)
In-Reply-To: <20170413133928.jmykwcq4qq5grktk@hirez.programming.kicks-ass.net>
On 13 April 2017 at 15:39, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Apr 11, 2017 at 09:52:21AM +0200, Vincent Guittot wrote:
>
>> > Secondly, what's up with the util_sum < LOAD_AVG_MAX * 1000 thing?
>>
>> The lost idle time makes sense only if the task can also be "idle"
>> when running at max capacity. When util_sum reaches the
>> LOAD_AVG_MAX*SCHED_CAPACITY_SCALE value, all tasks are considered to
>> be the same as we can't make any difference between a task running
>> 400ms or a task running 400sec. It means that these tasks are "always
>> running" tasks even at max capacity. In this case, there is no lost
>> idle time as they always run and tracking and adding back the lost
>> idle time because we run at lower capacity doesn't make sense anymore
>> so we discard it.
>
> Right, this is the point we reached yesterday with the too low F. At
> that point you cannot know and we assuming u=1, F<1 -> u=1, F=1, which
> is a sensible assumption.
>
>> Then an always running task can have a util_sum that is less than the
>> max value because of the rounding (util_avg varies between
>> [1006..1023]), so I use LOAD_AVG_MAX*1000 instead of LOAD_AVG_MAX*1024
>
> OK, so the reason util_avg varies is because we compute it wrong. And I
> think we can easily fix that once we pull out all the factors (which
> would mean your patch and the pulling out of weight patch which still
> needs to be finished).
That would be great to remove this unwanted variation.
>
> But you're comparing against util_sum here, that behaves slightly
> different. I think you want 'util_sum >= 1024 * (LOAD_AVG_MAX - 1024)'
> instead.
yes, the variation happens on the util_sum
next prev parent reply other threads:[~2017-04-13 15:16 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-10 9:18 [PATCH v2] sched/fair: update scale invariance of PELT Vincent Guittot
2017-04-10 17:38 ` Peter Zijlstra
2017-04-11 7:52 ` Vincent Guittot
2017-04-11 8:53 ` Peter Zijlstra
2017-04-11 9:40 ` Vincent Guittot
2017-04-11 10:41 ` Peter Zijlstra
2017-04-11 10:49 ` Peter Zijlstra
2017-04-11 13:09 ` Vincent Guittot
2017-04-12 11:28 ` Peter Zijlstra
2017-04-12 14:50 ` Vincent Guittot
2017-04-12 15:44 ` Peter Zijlstra
2017-04-13 9:42 ` Vincent Guittot
2017-04-13 13:32 ` Peter Zijlstra
2017-04-13 14:59 ` Vincent Guittot
2017-04-13 18:06 ` Peter Zijlstra
2017-04-14 8:47 ` Vincent Guittot
2017-04-11 12:08 ` Vincent Guittot
2017-04-11 9:12 ` Peter Zijlstra
2017-04-11 9:46 ` Vincent Guittot
2017-04-13 13:39 ` Peter Zijlstra
2017-04-13 15:16 ` Vincent Guittot [this message]
2017-04-13 16:13 ` Peter Zijlstra
2017-04-14 8:49 ` Vincent Guittot
2017-04-19 16:31 ` Vincent Guittot
2017-04-28 15:52 ` Morten Rasmussen
2017-04-28 17:08 ` Dietmar Eggemann
2017-05-03 17:11 ` Vincent Guittot
2017-04-28 22:09 ` Peter Zijlstra
2017-05-01 9:00 ` Peter Zijlstra
2017-05-02 13:38 ` Vincent Guittot
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=CAKfTPtANR173Hr1K4TOR1DbD6N6qty8V0eTgbKmVmfQUxkJ0Zw@mail.gmail.com \
--to=vincent.guittot@linaro.org \
--cc=Morten.Rasmussen@arm.com \
--cc=bsegall@google.com \
--cc=dietmar.eggemann@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=pjt@google.com \
--cc=yuyang.du@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).