linux-kernel - Re: [PATCH 1/2] sched/wait: Break up long wake list walk

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Message-ID: <CA+55aFxJ4x3przA6acW5qGZ-+MWSYTw0h6UjWH-D1xHcb9gnZw@mail.gmail.com>
Date:   Tue, 22 Aug 2017 13:58:59 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk

On Tue, Aug 22, 2017 at 1:53 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> So _the_ problem with yield() is when you hit this with a RT task it
> will busy spin and possibly not allow the task that actually has the
> lock to make progress at all.

I thought we had explicitly defined yield() to not do that.

But I guess we could make this yielding behavior depend on a few more
heuristics. So do the yield only when there is contention, and when
it's a non-RT task.

          Linus