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

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Date:	Fri, 14 Mar 2008 14:08:36 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.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, 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?

> 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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