Date:	Thu, 11 Oct 2012 16:56:11 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <pzijlstr@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hillf Danton <dhillf@...il.com>,
	Andrew Jones <drjones@...hat.com>,
	Dan Smith <danms@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Christoph Lameter <cl@...ux.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 00/33] AutoNUMA27

Hi Mel,

On Thu, Oct 11, 2012 at 11:19:30AM +0100, Mel Gorman wrote:
> As a basic sniff test I added a test to MMtests for the AutoNUMA
> Benchmark on a 4-node machine and the following fell out.
> 
>                                      3.6.0                 3.6.0
>                                    vanilla        autonuma-v33r6
> User    SMT             82851.82 (  0.00%)    33084.03 ( 60.07%)
> User    THREAD_ALLOC   142723.90 (  0.00%)    47707.38 ( 66.57%)
> System  SMT               396.68 (  0.00%)      621.46 (-56.67%)
> System  THREAD_ALLOC      675.22 (  0.00%)      836.96 (-23.95%)
> Elapsed SMT              1987.08 (  0.00%)      828.57 ( 58.30%)
> Elapsed THREAD_ALLOC     3222.99 (  0.00%)     1101.31 ( 65.83%)
> CPU     SMT              4189.00 (  0.00%)     4067.00 (  2.91%)
> CPU     THREAD_ALLOC     4449.00 (  0.00%)     4407.00 (  0.94%)

Thanks a lot for the help and for looking into it!

Just curious, why are you running only numa02_SMT and
numa01_THREAD_ALLOC? And not numa01 and numa02? (the standard version
without _suffix)

> 
> The performance improvements are certainly there for this basic test but
> I note the System CPU usage is very high.

Yes, migrate is expensive, but after convergence has been reached the
system time should be the same as upstream.

btw, I improved things further in autonuma28 (new branch in aa.git).

> 
> The vmstats showed up this
> 
> THP fault alloc               81376       86070
> THP collapse alloc               14       40423
> THP splits                        8       41792
> 
> So we're doing a lot of splits and collapses for THP there. There is a
> possibility that khugepaged and the autonuma kernel thread are doing some
> busy work. Not a show-stopped, just interesting.
> 
> I've done no analysis at all and this was just to have something to look
> at before looking at the code closer.

Sure, the idea is to have THP native migration, then we'll do zero
collapse/splits.

> > The objective of AutoNUMA is to provide out-of-the-box performance as
> > close as possible to (and potentially faster than) manual NUMA hard
> > bindings.
> > 
> > It is not very intrusive into the kernel core and is well structured
> > into separate source modules.
> > 
> > AutoNUMA was extensively tested against 3.x upstream kernels and other
> > NUMA placement algorithms such as numad (in userland through cpusets)
> > and schednuma (in kernel too) and was found superior in all cases.
> > 
> > Most important: not a single benchmark showed a regression yet when
> > compared to vanilla kernels. Not even on the 2 node systems where the
> > NUMA effects are less significant.
> > 
> 
> Ok, I have not run a general regression test and won't get the chance to
> soon but hopefully others will. One thing they might want to watch out
> for is System CPU time. It's possible that your AutoNUMA benchmark
> triggers a worst-case but it's worth keeping an eye on because any cost
> from that has to be offset by gains from better NUMA placements.

Good idea to monitor it indeed.

> Is STREAM really a good benchmark in this case? Unless you also ran it in
> parallel mode, it basically operations against three arrays and not really
> NUMA friendly once the total size is greater than a NUMA node. I guess
> it makes sense to run it just to see does autonuma break it :)

The way this is run is that there is 1 stream, then 4 stream, then 8
until we max out all CPUs.

I think we could run "memhog" instead of "stream" and it'd be the
same. stream probably better resembles real life computations.

The upstream scheduler lacks any notion of affinity so eventually
during the 5 min run, on process changes node, it doesn't notice its
memory was elsewhere so it stays there, and the memory can't follow
the cpu either. So then it runs much slower.

So it's the simplest test of all to get right, all it requires is some
notion of node affinity.

It's also the only workload that the home node design in schednuma in
tip.git can get right (schednuma post current tip.git introduced
cpu-follow-memory design of AutoNUMA so schednuma will have a chance
to get right more stuff than just the stream multi instance
benchmark).

So it's just for a verification than the simple stuff (single threaded
process computing) is ok and the upstream regression vs hard NUMA
bindings is fixed.

stream is also one case where we have to perform identical to the hard
NUMA bindings. No migration of CPU or memory must ever happen with
AutoNUMA in the stream benchmark. AutoNUMA will just monitor it and
find that it is already in the best place and it will leave it alone.

With the autonuma-benchmark it's impossible to reach identical
performance of the _HARD_BIND case because _HARD_BIND doesn't need to
do any memory migration (I'm 3 seconds away from hard bindings in a
198 sec run though, just the 3 seconds it takes to migrate 3g of ram ;).

> 
> > 
> > == iozone ==
> > 
> >                      ALL  INIT   RE             RE   RANDOM RANDOM BACKWD  RECRE STRIDE  F      FRE     F      FRE
> > FILE     TYPE (KB)  IOS  WRITE  WRITE   READ   READ   READ  WRITE   READ  WRITE   READ  WRITE  WRITE   READ   READ
> > ====--------------------------------------------------------------------------------------------------------------
> > noautonuma ALL      2492   1224   1874   2699   3669   3724   2327   2638   4091   3525   1142   1692   2668   3696
> > autonuma   ALL      2531   1221   1886   2732   3757   3760   2380   2650   4192   3599   1150   1731   2712   3825
> > 
> > AutoNUMA can't help much for I/O loads but you can see it seems a
> > small improvement there too. The important thing for I/O loads, is to
> > verify that there is no regression.
> > 
> 
> It probably is unreasonable to expect autonuma to handle the case where
> a file-based workload has not been tuned for NUMA. In too many cases
> it's going to be read/write based so you're not going to get the
> statistics you need.

Agreed. Some statistic may still accumulate and it's still better than
nothing but unless the workload is CPU and memory bound, we can't
expect to see any difference.

This is meant as a verification that we're not introducing regression
to I/O bound load.

Andrea
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