Re: [Bug #15713] hackbench regression due to commit 9dfc6e68bfe6e

Tejun Heo
2010-04-26T10:03:40Z

Hello,

On 04/26/2010 09:22 AM, Pekka Enberg wrote:
> On Mon, Apr 26, 2010 at 9:59 AM, Zhang, Yanmin
> <yanmin_zhang@linux.intel.com> wrote:
>>> I haven't been able to reproduce this either on my Core 2 machine.
>> Mostly, the regression exists on Nehalem machines. I suspect it's related to
>> hyper-threading machine.
>
> OK, so does anyone know why hyper-threading would change things for
> the per-CPU allocator?

My wild speculation is that previously the cpu_slub structures of two
neighboring threads ended up on the same cacheline by accident thanks
to the back to back allocation. W/ the percpu allocator, this no
longer would happen as the allocator groups percpu data together
per-cpu.

Thanks.

--
tejun