Re: SLAB vs. SLUB tbench regression (Was: [tbench regression fixes]: digging out smelly deadmen.)

Pekka Enberg
2008-10-31T15:09:01Z

On Fri, Oct 31, 2008 at 4:28 PM, Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> Hi Evgeniy,
>
> On Fri, Oct 10, 2008 at 1:17 AM, Evgeniy Polyakov
> <s0mbre@tservice.net.ru> wrote:
>> It was reported recently that tbench has a long history of regressions,
>> starting at least from 2.6.23 kernel. I verified that in my test
>> environment tbench 'lost' more than 100 MB/s from 470 down to 355
>> between at least 2.6.24 and 2.6.27. 2.6.26-2.6.27 performance regression
>> in my machines is rougly corresponds to 375 down to 355 MB/s.
>
> As you've already pointed out in private and in your blog, some part
> of the tbench regression comes from SLUB vs. SLAB as well. Looks like
> I can reproduce the regression locally as well:
>
> [ 8 clients and tbench_srv on the same machine on 2-way x86-64 ]
>
> min max avg sd
> 2.6.28-rc2-slab 234.57 244.88 242.68 0.71
> 2.6.28-rc2-slub 227.44 240.90 239.08 0.78

Christoph asked me to throw in the prefetch patch from Eric Dumazet.
Unfortunately, it doesn't seem to make much of a difference:

[ 2-way x86-64 with 8 clients and tbench_srv on the same machine ]

min max avg sd
2.6.28-rc2-slab 234.57 244.88 242.68 0.71
2.6.28-rc2-slub 227.44 240.90 239.08 0.78
2.6.28-rc2-slub+prefetch 237.42 244.32 239.78 0.92