From: changhuaixin <changhuaixin@linux.alibaba.com>
To: Odin Ugedal <odin@uged.al>
Cc: changhuaixin <changhuaixin@linux.alibaba.com>,
Benjamin Segall <bsegall@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
dtcccc@linux.alibaba.com, Juri Lelli <juri.lelli@redhat.com>,
khlebnikov@yandex-team.ru,
open list <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@suse.de>, Ingo Molnar <mingo@redhat.com>,
pauld@redhead.com, Peter Zijlstra <peterz@infradead.org>,
Paul Turner <pjt@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
shanpeic@linux.alibaba.com, Tejun Heo <tj@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
xiyou.wangcong@gmail.com
Subject: Re: [PATCH v5 2/3] sched/fair: Add cfs bandwidth burst statistics
Date: Fri, 21 May 2021 20:42:27 +0800 [thread overview]
Message-ID: <E4AA746E-6608-4576-BF19-57589B2867FE@linux.alibaba.com> (raw)
In-Reply-To: <CAFpoUr1GZspG1yKHf3D=+BZKfufWNNdu2Ccuj+YBo8EaJYRi8w@mail.gmail.com>
> On May 20, 2021, at 10:11 PM, Odin Ugedal <odin@uged.al> wrote:
>
> I am a bit sceptical about both the nr_burst and burst_time as they are now.
>
> As an example; a control group using "99.9%" of the quota each period
> and that is never throttled. Such group would with this patch with a burst of X
> still get nr_throttled = 0 (as before), but it would get a nr_burst
> and burst_time that
> will keep increasing.
>
Agreed, there are false positive and false negetive cases, as the current implementation
uses cfs_b->runtime to judge instead of the actual runtime used.
> I think there is a big difference between runtime moved/taken from
> cfs_b->runtime to cfs_rq->runtime_remaining and the actual runtime used
> in the period. Currently, cfs bw can only supply info the first one, and
> not the latter.
>
> I think that if people see nr_burst increasing, that they think they _have_
> to use cfs burst in order to avoid being throttled, even though that might
> not be the case. It is probably fine as is, as long as it is explicitly stated
It can't be seeing nr_burst incresing first, and using cfs burst feature afterwards.
Do you mean people see nr_throttled increasing and use cfs burst, while the actual usage
is below quota? In that case, tasks get throttled because there are runtime to be returned from
cfs_rq, and get unthrottled shortly. That is a false positive for nr_throttled. When users see that,
using burst can help improve.
> what the values mean and imply, and what they do not. I cannot see another
> way to calculate it as it is now, but maybe someone else has some thoughts.
>
> Thanks
> Odin
next prev parent reply other threads:[~2021-05-21 12:41 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-20 12:34 [PATCH v5 0/3] sched/fair: Burstable CFS bandwidth controller Huaixin Chang
2021-05-20 12:34 ` [PATCH v5 1/3] sched/fair: Introduce the burstable CFS controller Huaixin Chang
2021-05-20 14:00 ` Odin Ugedal
2021-05-20 17:04 ` Tejun Heo
2021-05-21 9:09 ` changhuaixin
2021-05-21 9:38 ` Odin Ugedal
2021-05-21 12:38 ` changhuaixin
2021-05-21 14:00 ` Peter Zijlstra
2021-05-24 12:42 ` changhuaixin
2021-05-25 10:46 ` Peter Zijlstra
2021-05-31 6:59 ` luca abeni
2021-05-25 10:47 ` Peter Zijlstra
2021-05-25 21:25 ` Benjamin Segall
2021-05-25 10:49 ` Peter Zijlstra
2021-05-20 12:34 ` [PATCH v5 2/3] sched/fair: Add cfs bandwidth burst statistics Huaixin Chang
2021-05-20 14:11 ` Odin Ugedal
2021-05-21 12:42 ` changhuaixin [this message]
2021-05-21 14:05 ` Peter Zijlstra
2021-05-20 17:06 ` Tejun Heo
2021-05-21 14:01 ` Peter Zijlstra
2021-05-20 12:34 ` [PATCH v5 3/3] sched/fair: Add document for burstable CFS bandwidth Huaixin Chang
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