linux-kernel - Re: Help Resource Counters Scale Better (v3)

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Date:	Mon, 10 Aug 2009 14:06:02 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, andi.kleen@...el.com,
	Prarit Bhargava <prarit@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"menage@...gle.com" <menage@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Help Resource Counters Scale Better (v3)

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-08-10 15:22:05]:

> On Mon, 10 Aug 2009 14:45:59 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> 
> > > Do you agree?
> > 
> > Ok. Config is enough at this stage.
> > 
> > The last advice for merge is, it's better to show the numbers or
> > ask someone who have many cpus to measure benefits. Then, Andrew can
> > know how this is benefical.
> > (My box has 8 cpus. But maybe your IBM collaegue has some bigger one)
> > 
> > In my experience (in my own old trial),
> >  - lock contention itself is low. not high.
> >  - but cacheline-miss, pingpong is very very frequent.
> > 
> > Then, this patch has some benefit logically but, in general,
> > File-I/O, swapin-swapout, page-allocation/initalize etc..dominates
> > the performance of usual apps. You'll have to be careful to select apps
> > to measure the benfits of this patch by application performance.
> > (And this is why I don't feel so much emergency as you do)
> > 
> 
> Why I say "I want to see the numbers" again and again is that
> this is performance improvement with _bad side effect_.
> If this is an emergent trouble, and need fast-track, which requires us
> "fix small problems later", plz say so. 
>

OK... I finally got a bigger machine (24 CPUs). I ran a simple
program called parallel_pagefault, which does pagefault's in parallel
(runs on every other CPU) and allocates 10K pages and touches the
data allocated, unmaps and repeats the process. I ran the program
for 300 seconds. With the patch, I was able to fault in twice
the number of pages as I was able to without the patch. I used
perf tool from tools/perf in the kernel

With patch

 Performance counter stats for '/home/balbir/parallel_pagefault':

 7188177.405648  task-clock-msecs         #     23.926 CPUs 
         423130  context-switches         #      0.000 M/sec
            210  CPU-migrations           #      0.000 M/sec
       49851597  page-faults              #      0.007 M/sec
  5900210219604  cycles                   #    820.821 M/sec
   424658049425  instructions             #      0.072 IPC  
     7867744369  cache-references         #      1.095 M/sec
     2882370051  cache-misses             #      0.401 M/sec

  300.431591843  seconds time elapsed

Without Patch

 Performance counter stats for '/home/balbir/parallel_pagefault':

 7192804.124144  task-clock-msecs         #     23.937 CPUs 
         424691  context-switches         #      0.000 M/sec
            267  CPU-migrations           #      0.000 M/sec
       28498113  page-faults              #      0.004 M/sec
  5826093739340  cycles                   #    809.989 M/sec
   408883496292  instructions             #      0.070 IPC  
     7057079452  cache-references         #      0.981 M/sec
     3036086243  cache-misses             #      0.422 M/sec

  300.485365680  seconds time elapsed


-- 
	Balbir
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