linux-kernel - Re: numa/core regressions fixed

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Date:	Mon, 26 Nov 2012 10:11:20 +0800
From:	Alex Shi <lkml.alex@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>, Alex Shi <alex.shi@...el.com>
Subject: Re: numa/core regressions fixed - more testers wanted

On Fri, Nov 23, 2012 at 9:31 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Ingo Molnar <mingo@...nel.org> wrote:
>
>> * Alex Shi <lkml.alex@...il.com> wrote:
>>
>> > >
>> > > Those of you who would like to test all the latest patches are
>> > > welcome to pick up latest bits at tip:master:
>> > >
>> > >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master
>> > >
>> >
>> > I am wondering if it is a problem, but it still exists on HEAD: c418de93e39891
>> > http://article.gmane.org/gmane.linux.kernel.mm/90131/match=compiled+with+name+pl+and+start+it+on+my
>> >
>> > like when just start 4 pl tasks, often 3 were running on node
>> > 0, and 1 was running on node 1. The old balance will average
>> > assign tasks to different node, different core.
>>
>> This is "normal" in the sense that the current mainline
>> scheduler is (supposed to be) doing something similar: if the
>> node is still within capacity, then there's no reason to move
>> those threads.
>>
>> OTOH, I think with NUMA balancing we indeed want to spread
>> them better, if those tasks do not share memory with each
>> other but use their own memory. If they share memory then they
>> should remain on the same node if possible.

I rewrite the little test case by assemble:
==
.text

    .global _start

_start:

do_nop:
        nop
        nop
        jmp do_nop
==
It reproduced the problem on latest tip/master, HEAD: 7cb989d0159a6f43104992f18
like for 4 above tasks running, 3 of them running on node 0, one
running on node 1.

If kernel can detect the LLC of CPU is allowed for tasks aggregate, it's a nice
feature. if not, the aggregate may cause more cache missing.


>
> Could you please check tip:master with -v17:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master
>
> ?
>
> It should place your workload better than v16 did.
>
> Note, you might be able to find other combinations of tasks that
> are not scheduled NUMA-perfectly yet, as task group placement is
> not exhaustive yet.
>
> You might want to check which combination looks the weirdest to
> you and report it, so I can fix any remaining placement
> inefficiencies in order of importance.
>
> Thanks,
>
>         Ingo



-- 
Thanks
    Alex
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