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

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Date:	Thu, 5 Mar 2009 11:34:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Nick Piggin <npiggin@...e.de>, Mel Gorman <mel@....ul.ie>,
	Lin Ming <ming.m.lin@...el.com>,
	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


* 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?

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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