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

["Pekka Enberg" <penberg@cs.helsinki.fi>]

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