linux-kernel - Re: hackbench [pthread mode] regression with 2.6.29-rc3

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Date:	Sun, 01 Feb 2009 16:29:21 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	peterz@...radead.org
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: hackbench [pthread mode] regression with 2.6.29-rc3


> Bisect located below patch.
> commit 490dea45d00f01847ebebd007685d564aaf2cd98
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Mon Nov 24 17:06:57 2008 +0100
> 
>    itimers: remove the per-cpu-ish-ness
> 
>    Either we bounce once cacheline per cpu per tick, yielding n^2 bounces
>    or we just bounce a single..
> 
>    Also, using per-cpu allocations for the thread-groups complicates the
>    per-cpu allocator in that its currently aimed to be a fixed sized
>    allocator and the only possible extention to that would be vmap based,
>    which is seriously constrained on 32 bit archs.
> 
> 
> After above patch is reverted, hackbench result is restored.

oltp has ~3% regression with 2.6.29-rc3 on 4core*2p stokley machine.
After above patch reverted, the regression disappeared.

Lin Ming

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