linux-kernel - Re: hackbench regression due to commit 9dfc6e68bfe6e

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Message-ID: <i2z84144f021004051030k7ff5190cyc083aa12c552dfac@mail.gmail.com>
Date:	Mon, 5 Apr 2010 20:30:06 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>, alex.shi@...el.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Ma, Ling" <ling.ma@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: hackbench regression due to commit 9dfc6e68bfe6e

(I'm CC'ing Tejun)

On Mon, Apr 5, 2010 at 4:54 PM, Christoph Lameter
<cl@...ux-foundation.org> wrote:
> On Fri, 2 Apr 2010, Zhang, Yanmin wrote:
>
>> My testing command on my 2 socket machine:
>> #hackbench 100 process 20000
>>
>> With 2.6.33, it takes for about 96 seconds while 2.6.34-rc2 (or the latest tip tree)
>> takes for about 101 seconds.
>>
>> perf shows some functions around SLUB have more cpu utilization, while some other
>> SLUB functions have less cpu utilization.
>
> Hmnmmm... The dynamic percpu areas use page tables and that data is used
> in the fast path. Maybe the high thread count causes tlb trashing?

Hmm indeed. I don't see anything particularly funny in the SLUB percpu
conversion so maybe this is a more issue with the new percpu
allocator?
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