linux-kernel - Performance regression of specjbb2005/aim7 with 2.6.29-rc1

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Date:	Tue, 13 Jan 2009 16:57:16 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Mike Galbraith <efault@....de>
Cc:	LKML <linux-kernel@...r.kernel.org>, ming.m.lin@...el.com,
	Peter Zijlstra <peterz@...radead.org>
Subject: Performance regression of specjbb2005/aim7 with 2.6.29-rc1

Comparing with 2.6.28's results, specjbb2005 has about 7% regression with 2.6.29-rc1
on my a couple of x86_64 machines. aim7 has about 1.7% regression.

Ming did a quick bisect with aim7 and located below patch.

commit 0a582440ff546e2c6610d1acec325e91b4efd313
Author: Mike Galbraith <efault@....de>
Date:   Fri Jan 2 12:16:42 2009 +0100

    sched: fix sched_slice()

    Impact: fix bad-interactivity buglet

    Fix sched_slice() to emit a sane result whether a task is currently
    enqueued or not.

    Signed-off-by: Mike Galbraith <efault@....de>
    Tested-by: Jayson King <dev@...sonking.com>
    Signed-off-by: Ingo Molnar <mingo@...e.hu>

After we revert the patch, aim7 regression disappeared. specjbb2005 regression becomes
less than 1.5% on 8-core stokley and disappears on 16-core tigerton. I don't know what
causes the last 1.5% regression.

As tbench has about 5% improvement and oltp(mysql+sysbench) has 5% improvement, we also tested
to make sure such improvement isn't related to above patch. volanoMark's improvement is also not
related to the patch. So it seems safe to revert it.

yanmin

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