linux-kernel - hackbench regression with 2.6.26-rc2 on tulsa machine

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Date:	Tue, 20 May 2008 16:09:06 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Mike Galbraith <efault@....de>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: hackbench regression with 2.6.26-rc2 on tulsa machine

Comparing with 2.6.26-rc1, hackbench has about 30% regression with 2.6.26-rc2 on my tulsa machine
which is a netburst architecure hyper-threading x86_64.

Command line to test: #hackbench 100 process 2000

With 2.6.26-rc1, it takes 30 seconds. But with 2.6.26-rc2/rc3, it takes 40 seconds.

Bisect located below patch:
46151122e0a2e80e5a6b2889f595e371fe2b600d is first bad commit
commit 46151122e0a2e80e5a6b2889f595e371fe2b600d
Author: Mike Galbraith <efault@....de>
Date:   Thu May 8 17:00:42 2008 +0200

    sched: fix weight calculations
    
    The conversion between virtual and real time is as follows:
    
      dvt = rw/w * dt <=> dt = w/rw * dvt
    
    Since we want the fair sleeper granularity to be in real time, we actually
    need to do:
    
      dvt = - rw/w * l



The bisect steps look stable.

On my core architecure machines(stoakley and tigerton), I do see improvement instead of regression,
like result from 31 seconds down to 28 seconds.

I'm not sure if hyper-threading need more cares in this situation.

-yanmin


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