From: Tejun Heo <tj@kernel.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Mike Galbraith <efault@gmx.de>, Paul Turner <pjt@google.com>,
Chris Mason <clm@fb.com>,
kernel-team@fb.com
Subject: Re: [PATCH v2 for-4.12-fixes 2/2] sched/fair: Fix O(# total cgroups) in load balance path
Date: Fri, 12 May 2017 09:16:04 -0400 [thread overview]
Message-ID: <20170512131604.GA1161@wtj.duckdns.org> (raw)
In-Reply-To: <CAKfTPtDPDseGBts+nzk=GqONXcwP0ZhETFd1ygsmi7P3FJDK6Q@mail.gmail.com>
Hello, Vincent.
On Thu, May 11, 2017 at 09:02:22AM +0200, Vincent Guittot wrote:
> Sorry, what i mean is:
> When the group entity of a cfs_rq is enqueued, we are sure that either
> the parents is already enqueued or it will be enqueued in the same
> sequence. We must be sure that no other branch will be enqueued in the
> middle of the sequence and will reset tmp_alone_branch.
> This is true with current implementation but I wondered it can happen
> if we del/add the cfs_rq out of order
>
> That said i haven't find a use case that break the sequence
Hmm... a cfs_rq can be removed from leaf list iff it's empty and
dequeued, and enqueueing is always from top down. If an ancestor is
already enqueued, it's guaranteed to be on the leaf list; otherwise,
it's guaranteed to be enqueued beforehand and thus put on the leaf
list too. I think it should be fine.
Thanks.
--
tejun
next prev parent reply other threads:[~2017-05-12 13:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-09 16:17 [PATCH v2 for-4.12-fixes 1/2] sched/fair: Use task_groups instead of leaf_cfs_rq_list to walk all cfs_rqs Tejun Heo
2017-05-09 16:18 ` [PATCH v2 for-4.12-fixes 2/2] sched/fair: Fix O(# total cgroups) in load balance path Tejun Heo
2017-05-10 6:50 ` Vincent Guittot
2017-05-10 14:44 ` Tejun Heo
2017-05-10 15:55 ` Tejun Heo
2017-05-11 7:02 ` Vincent Guittot
2017-05-12 13:16 ` Tejun Heo [this message]
2017-05-12 14:36 ` Vincent Guittot
2017-05-10 17:36 ` [PATCH v3 " Tejun Heo
2017-05-24 23:40 ` [PATCH v2 for-4.12-fixes 1/2] sched/fair: Use task_groups instead of leaf_cfs_rq_list to walk all cfs_rqs Tim Chen
2017-05-25 14:39 ` Tejun Heo
2017-05-26 23:04 ` Tim Chen
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