linux-kernel - Re: hackbench regression since 2.6.25-rc

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Date:	Mon, 17 Mar 2008 11:05:36 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: hackbench regression since 2.6.25-rc

On Fri, 2008-03-14 at 14:08 -0700, Christoph Lameter wrote:
> On Fri, 14 Mar 2008, Zhang, Yanmin wrote:
> 
> > > Ahhh... Okay those slabs did not change for 2.6.25-rc. Is there
> > > really a difference to 2.6.24?
> > As oprofile shows slub functions spend more than 80% cpu time, I would like
> > to focus on optimizing SLUB before going back to 2.6.24.
> 
> I thought you wanted to address a regression vs 2.6.24?
Initially I wanted to do so, but oprofile data showed both 2.6.24 and 2.6.25-rc
aren't good with hachbench on tigerton.

The slub_min_objects boot parameter could boost performance largely. So I think
we need optimize it before addressing the regression.

> 
> > kmalloc-512: No NUMA information available.
> > 
> > Slab Perf Counter       Alloc     Free %Al %Fr
> > --------------------------------------------------
> > Fastpath             55039159  5006829  68   6
> > Slowpath             24975754 75007769  31  93
> > Page Alloc              73840    73779   0   0
> > Add partial                 0 24341085   0  30
> > Remove partial       24267297    73779  30   0
> 
> ^^^ add partial/remove partial is likely the cause for 
> trouble here. 30% is unacceptably high. The larger allocs will reduce the 
> partial handling overhead. That is likely the effect that we see here.
> 
> > Refill 24975738
> 
> Duh refills at 50%? We could try to just switch to another slab instead of 
> reusing the existing one. May also affect the add/remove partial 
> situation.
> 
> 
> 

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