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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Fri, 28 Dec 2018 19:04:23 +0100
Message-ID: <CAKfTPtBV6tkf237ZAtWrHAYAiK+o3m_cd7ctX3EeLzt+onzUZQ@mail.gmail.com>
Subject: Re: [PATCH] sched: fix infinity loop in update_blocked_averages
To:     Tejun Heo <tj@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Sargun Dhillon <sargun@sargun.me>,
        Xie XiuQi <xiexiuqi@huawei.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, xiezhipeng1@huawei.com,
        huawei.libin@huawei.com,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Dmitry Adamushko <dmitry.adamushko@gmail.com>,
        Rik van Riel <riel@surriel.com>
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On Fri, 28 Dec 2018 at 18:46, Tejun Heo <tj@kernel.org> wrote:
>
> On Fri, Dec 28, 2018 at 06:25:37PM +0100, Vincent Guittot wrote:
> > > done without extra space as long as each node has the parent pointer,
> > > which they do.  Is the dedicated list an optimization?
> >
> > It prevents to parse and walk all task group struct every time.
> > Instead, you just have to follow a linked list
>
> Hmmm... I'm having a bit of a hard time imagining doing an actual
> traversal being a meaningful optimization.  It may require more
> branches but that shouldn't be expensive at all, especially compared
> to walking all idle groups in the system each time which the code used
> to do. Anyways, this is tangential.
>
> Thanks for the explanation and happy new year!

Happy new year for you too

Thanks
Vincent

>
> --
> tejun