linux-kernel - Re: [RFC PATCH 00/19] Cleanup and optimise the page allocator V2

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Message-Id: <1236328388.11608.35.camel@minggr.sh.intel.com>
Date:	Fri, 06 Mar 2009 16:33:08 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Nick Piggin <npiggin@...e.de>, Mel Gorman <mel@....ul.ie>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 00/19] Cleanup and optimise the page allocator V2

On Thu, 2009-03-05 at 18:34 +0800, Ingo Molnar wrote:
> * Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> 
> > On Wed, 2009-03-04 at 10:07 +0100, Nick Piggin wrote:
> > > On Wed, Mar 04, 2009 at 10:05:07AM +0800, Zhang, Yanmin wrote:
> > > > On Mon, 2009-03-02 at 11:21 +0000, Mel Gorman wrote:
> > > > > (Added Ingo as a second scheduler guy as there are queries on tg_shares_up)
> > > > > 
> > > > > On Fri, Feb 27, 2009 at 04:44:43PM +0800, Lin Ming wrote:
> > > > > > On Thu, 2009-02-26 at 19:22 +0800, Mel Gorman wrote: 
> > > > > > > In that case, Lin, could I also get the profiles for UDP-U-4K please so I
> > > > > > > can see how time is being spent and why it might have gotten worse?
> > > > > > 
> > > > > > I have done the profiling (oltp and UDP-U-4K) with and without your v2
> > > > > > patches applied to 2.6.29-rc6.
> > > > > > I also enabled CONFIG_DEBUG_INFO so you can translate address to source
> > > > > > line with addr2line.
> > > > > > 
> > > > > > You can download the oprofile data and vmlinux from below link,
> > > > > > http://www.filefactory.com/file/af2330b/
> > > > > > 
> > > > > 
> > > > > Perfect, thanks a lot for profiling this. It is a big help in figuring out
> > > > > how the allocator is actually being used for your workloads.
> > > > > 
> > > > > The OLTP results had the following things to say about the page allocator.
> > > > In case we might mislead you guys, I want to clarify that here OLTP is
> > > > sysbench (oltp)+mysql, not the famous OLTP which needs lots of disks and big
> > > > memory.
> > > > 
> > > > Ma Chinang, another Intel guy, does work on the famous OLTP running.
> > > 
> > > OK, so my comments WRT cache sensitivity probably don't apply here,
> > > but probably cache hotness of pages coming out of the allocator
> > > might still be important for this one.
> > Yes. We need check it.
> > 
> > > 
> > > How many runs are you doing of these tests?
> > We start sysbench with different thread number, for example, 8 12 16 32 64 128 for
> > 4*4 tigerton, then get an average value in case there might be a scalability issue.
> > 
> > As for this sysbench oltp testing, we reran it for 7 times on 
> > tigerton this week and found the results have fluctuations. 
> > Now we could only say there is a trend that the result with 
> > the pathces is a little worse than the one without the 
> > patches.
> 
> Could you try "perfstat -s" perhaps and see whether any other of 
> the metrics outside of tx/sec has less natural noise?

Thanks, I have used "perfstat -s" to collect cache misses data.

2.6.29-rc7-tip: tip/perfcounters/core (b5e8acf)
2.6.29-rc7-tip-mg2: v2 patches applied to tip/perfcounters/core

I collected 5 times netperf UDP-U-4k data with and without mg-v2 patches
applied to tip/perfcounters/core on a 4p quad-core tigerton machine, as
below
"value" means UDP-U-4k test result.

2.6.29-rc7-tip
---------------
value           cache misses    CPU migrations  cachemisses/migrations
5329.71          391094656       1710            228710
5641.59          239552767       2138            112045
5580.87          132474745       2172            60992
5547.19          86911457        2099            41406
5626.38          196751217       2050            95976

2.6.29-rc7-tip-mg2
-------------------
value           cache misses    CPU migrations  cachemisses/migrations
4749.80          649929463       1132            574142
4327.06          484100170       1252            386661
4649.51          374201508       1489            251310
5655.82          405511551       1848            219432
5571.58          90222256        2159            41788

Lin Ming

> 
> I think a more invariant number might be the ratio of "LLC 
> cachemisses" divided by "CPU migrations".
> 
> The fluctuation in tx/sec comes from threads bouncing - but you 
> can normalize that away by using the cachemisses/migrations 
> ration.
> 
> Perhaps. It's definitely a difficult thing to measure.
> 
> 	Ingo

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