linux-kernel - dbench 15% regression with 2.6.28-rc1

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Message-Id: <1225183290.1685.73.camel@ymzhang>
Date:	Tue, 28 Oct 2008 16:41:30 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: dbench 15% regression with 2.6.28-rc1

Comparing with 2.6.27, dbench result has regression with 2.6.28-rc1 on 2 machines.
1) 8-core stoakley: 15%
2) 8 core+mutl-thread new-model x86-64: 12%

Bisect located below patch.

695698500912c4479ddf4723e492de3970ff8530 is first bad commit
commit 695698500912c4479ddf4723e492de3970ff8530
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date:   Tue Sep 23 14:54:23 2008 +0200

    sched: rework wakeup preemption

    Rework the wakeup preemption to work on real runtime instead of
    the virtual runtime. This greatly simplifies the code.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
    Signed-off-by: Ingo Molnar <mingo@...e.hu>

I reverted the patch against 2.6.28-rc2 and the regression mostly disappears
on 8-core stoakley and 8-core+multiThread x86-64 machines.

On other 2 machines, I see improvement instead of regression.
1) 16-core tigerton: improvement 48%
2) 8-core+hyperThreading tulsa: 10%.
I just checked it by reverting above patch to see if the patch improves it. At least
it isn't on tigerton. I'm doing a new bisect on tigerton to see what patch improves
dbench result.

I start online cpu number of dbench processes.

-yanmin

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