linux-kernel - Re: Problem: scaling of /proc/stat on large systems

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Message-Id: <20101012090907.5dd1cf57.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 12 Oct 2010 09:09:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Jack Steiner <steiner@....com>
Cc:	yinghai@...nel.org, mingo@...e.hu, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: Problem: scaling of /proc/stat on large systems

On Fri, 8 Oct 2010 11:35:57 -0500
Jack Steiner <steiner@....com> wrote:

> On Tue, Oct 05, 2010 at 05:19:07PM +0900, KAMEZAWA Hiroyuki wrote:
> > On Tue, 5 Oct 2010 10:36:50 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > 
> > > I guess this requres different approarch as per-cpu counter + threshould.
> > > like vmstat[] or lib/percpu_counter. 
> > > Maybe people don't like to access shared counter in IRQ.
> > > 
> > > But, this seems to call radixtree-lookup for the # of possible cpus.
> > > I guess impleimenting a call to calculate a sum of irqs in a radix-tree
> > > lookup will reduce overhead. If it's not enough, we'll have to make the
> > > counter not-precise. I'll write an another patch.
> > > 
> > 
> > How about this ? This is an add-on patch.
> 
> Nice!!
> 
> The combination of the 2 patches solves the problem.
> The timings are (4096p, 256 nodes, 4592 irqs):
> 
> 	# time cat /proc/stat > /dev/null
> 
> 	Baseline:		12.627 sec
> 	Patch1  :		 2.459 sec
> 	Patch 1 + Patch 2:	  .561 sec
> 
> 
> Acked-by: Jack Steiner <steiner@....com>
> 

Thank you for testing. I'll post again if necessary.

-Kame


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