linux-kernel - Re: [PATCH 00/46] Automatic NUMA Balancing V4

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Date:	Wed, 21 Nov 2012 19:21:58 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Alex Shi <lkml.alex@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/46] Automatic NUMA Balancing V4


* Mel Gorman <mgorman@...e.de> wrote:

> On Wed, Nov 21, 2012 at 06:33:16PM +0100, Ingo Molnar wrote:
> > 
> > * Mel Gorman <mgorman@...e.de> wrote:
> > 
> > > On Wed, Nov 21, 2012 at 06:03:06PM +0100, Ingo Molnar wrote:
> > > > 
> > > > * Mel Gorman <mgorman@...e.de> wrote:
> > > > 
> > > > > On Wed, Nov 21, 2012 at 10:21:06AM +0000, Mel Gorman wrote:
> > > > > > 
> > > > > > I am not including a benchmark report in this but will be posting one
> > > > > > shortly in the "Latest numa/core release, v16" thread along with the latest
> > > > > > schednuma figures I have available.
> > > > > > 
> > > > > 
> > > > > Report is linked here https://lkml.org/lkml/2012/11/21/202
> > > > > 
> > > > > I ended up cancelling the remaining tests and restarted with
> > > > > 
> > > > > 1. schednuma + patches posted since so that works out as
> > > > 
> > > > Mel, I'd like to ask you to refer to our tree as numa/core or 
> > > > 'numacore' in the future. Would such a courtesy to use the 
> > > > current name of our tree be possible?
> > > > 
> > > 
> > > Sure, no problem.
> > 
> > Thanks!
> > 
> > I ran a quick test with your 'balancenuma v4' tree and while 
> > numa02 and numa01-THREAD-ALLOC performance is looking good, 
> > numa01 performance does not look very good:
> > 
> >                     mainline    numa/core      balancenuma-v4
> >      numa01:           340.3       139.4          276 secs
> > 
> > 97% slower than numa/core.
> > 
> 
> It would be. numa01 is an adverse workload where all threads 
> are hammering the same memory.  The two-stage filter in 
> balancenuma restricts the amount of migration it does so it 
> ends up in a situation where it cannot balance properly. [...]

Do you mean this "balancenuma v4" patch attributed to you:

 Subject: mm: Numa: Use a two-stage filter to restrict pages being migrated for unlikely task<->node relationships
 From: Mel Gorman <mgorman@...e.de>
 Date: Wed, 21 Nov 2012 10:21:42 +0000

 ...

 Signed-off-by: Mel Gorman <mgorman@...e.de>

which has:

                /*
                 * Multi-stage node selection is used in conjunction
                 * with a periodic migration fault to build a temporal
                 * task<->page relation. By using a two-stage filter we
                 * remove short/unlikely relations.
                 *
                 * Using P(p) ~ n_p / n_t as per frequentist
                 * probability, we can equate a task's usage of a
                 * particular page (n_p) per total usage of this
                 * page (n_t) (in a given time-span) to a probability.
                 *
                 * Our periodic faults will sample this probability and
                 * getting the same result twice in a row, given these
                 * samples are fully independent, is then given by
                 * P(n)^2, provided our sample period is sufficiently
                 * short compared to the usage pattern.
                 *
                 * This quadric squishes small probabilities, making
                 * it less likely we act on an unlikely task<->page
                 * relation.

This looks very similar to the code and text that Peter wrote 
for numa/core:

/*
 * Multi-stage node selection is used in conjunction with a periodic
 * migration fault to build a temporal task<->page relation. By
 * using a two-stage filter we remove short/unlikely relations.
 *
 * Using P(p) ~ n_p / n_t as per frequentist probability, we can
 * equate a task's usage of a particular page (n_p) per total usage
 * of this page (n_t) (in a given time-span) to a probability.
 *
 * Our periodic faults will then sample this probability and getting
 * the same result twice in a row, given these samples are fully
 * independent, is then given by P(n)^2, provided our sample period
 * is sufficiently short compared to the usage pattern.
 *
 * This quadric squishes small probabilities, making it less likely
 * we act on an unlikely task<->page relation.
 *
 * Return the best node ID this page should be on, or -1 if it should
 * stay where it is.
 */

see commit:

  30f93abc6cb3 sched, numa, mm: Add the scanning page fault machinery

?

I think it's the very same concept - yours is taken from an 
older sched/numa commit and attributed to yourself? [If so then 
please fix the attribution.]

We have the same filter in numa/core - because we wrote it (FYI, 
I wrote bits of the last_cpu variant in numa/core), yet our 
numa01 performance is much better than the one of balancenuma.

Thanks,

	Ingo
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