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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 18 Aug 2017 13:10:04 -0700
Message-ID: <CA+55aFxUMmHAQ1HZnFv20cM2Gh-VqH1oe833+ug0OORjqkqgqQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] sched/wait: Break up long wake list walk
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To: Andi Kleen <ak@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>, "Liang, Kan" <kan.liang@intel.com>, Mel Gorman <mgorman@suse.de>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Tim Chen <tim.c.chen@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, Jan Kara <jack@suse.cz>, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>

On Fri, Aug 18, 2017 at 12:58 PM, Andi Kleen <ak@linux.intel.com> wrote:
>> which is hacky, but there's a rationale for it:
>>
>>  (a) avoid the crazy long wait queues ;)
>>
>>  (b) we know that migration is *supposed* to be CPU-bound (not IO
>> bound), so yielding the CPU and retrying may just be the right thing
>> to do.
>
> So this would degenerate into a spin when the contention is with
> other CPUs?
>
> But then if we guarantee that migration has flat latency curve
> and no long tail it may be reasonable.

Honestly, right now I'd say it's more of a "poath meant purely for
testing with some weak-ass excuse for why it might not be broken".

                 Linus

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