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

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Message-ID: <84144f020810310808p9d6ecf9k6f10a671c21bf0da@mail.gmail.com>
Date:	Fri, 31 Oct 2008 17:08:32 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Evgeniy Polyakov" <s0mbre@...rvice.net.ru>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Ingo Molnar" <mingo@...e.hu>,
	"David Miller" <davem@...emloft.net>,
	"Christoph Lameter" <cl@...ux-foundation.org>,
	"Matthew Wilcox" <matthew@....cx>,
	"Eric Dumazet" <dada1@...mosbay.com>,
	"Nick Piggin" <nickpiggin@...oo.com.au>
Subject: Re: SLAB vs. SLUB tbench regression (Was: [tbench regression fixes]: digging out smelly deadmen.)

On Fri, Oct 31, 2008 at 4:28 PM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> Hi Evgeniy,
>
> On Fri, Oct 10, 2008 at 1:17 AM, Evgeniy Polyakov
> <s0mbre@...rvice.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
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