linux-kernel - 2.6.19-rc1: Slowdown in lmbench's fork

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Date:	Thu, 02 Nov 2006 08:44:57 -0800
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	ebiederm@...ssion.com
Subject: 2.6.19-rc1: Slowdown in lmbench's fork

After introduction of the following patch:

[PATCH] genirq: x86_64 irq: make vector_irq per cpu
http://kernel.org/git/?
p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=550f2299ac8ffaba943cf211380d3a8d3fa75301

we see fork benchmark in lmbench-3.0-a7 slowed by 
11.5% on a 2 socket woodcrest machine.  Similar change
is seen also on other SMP Xeon machines.

When running lmbench, we have chosen the lmbench option
to pin parent and child on different processor cores 

Overhead of calling sched_setaffinity to place the process 
on processor is included in lmbench's fork time measurement. 
The patch may play a role in increasing this.

The two follow up patches to the original "make vector_irq per cpu" 
did not affect the fork time.

[PATCH] x86_64 irq: Properly update vector_irq
[PATCH] x86-64: Only look at per_cpu data for online ...

Tim
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