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

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Message-ID: <84144f020810310728j1f3b8a99se428ec55b0c165b5@mail.gmail.com>
Date:	Fri, 31 Oct 2008 16:28:57 +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>
Subject: SLAB vs. SLUB tbench regression (Was: [tbench regression fixes]: digging out smelly deadmen.)

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

Oprofile seems to be busted for 2.6.28-rc2 so I'll follow up on this
as soon as that's settled.

Btw, just as one more data point, I accidentally tested with just 2
clients at first and SLUB actually beat SLAB.

                        Pekka
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