linux-kernel - hackbench regression since 2.6.25-rc

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Message-Id: <1205394417.3215.85.camel@ymzhang>
Date:	Thu, 13 Mar 2008 15:46:57 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: hackbench regression since 2.6.25-rc

Comparing with 2.6.24, on my 16-core tigerton, hackbench process mode has about
40% regression with 2.6.25-rc1, and more than 20% regression with kernel
2.6.25-rc4, because rc4 includes the reverting patch of scheduler load balance.

Command to start it.
#hackbench 100 process 2000
I ran it for 3 times and sum the values.

I tried to investiagte it by bisect.
Kernel up to tag 0f4dafc0563c6c49e17fe14b3f5f356e4c4b8806 has the 20% regression.
Kernel up to tag 6e90aa972dda8ef86155eefcdbdc8d34165b9f39 hasn't regression.

Any bisect between above 2 tags cause kernel hang. I tried to checkout to a point between
these 2 tags for many times manually and kernel always paniced.

All patches between the 2 tags are on kobject restructure. I guess such restructure
creates more cache miss on the 16-core tigerton.

Any idea?

-yanmin

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