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Date: Mon, 5 Apr 2010 20:30:06 +0300
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Subject: Re: hackbench regression due to commit 9dfc6e68bfe6e
From: Pekka Enberg <penberg@cs.helsinki.fi>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>, alex.shi@intel.com,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "Ma, Ling" <ling.ma@intel.com>, "Chen, Tim C" <tim.c.chen@intel.com>,
       Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>
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(I'm CC'ing Tejun)

On Mon, Apr 5, 2010 at 4:54 PM, Christoph Lameter
<cl@linux-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?