RE: Regression in reading /proc/stat in the newer kernels withlarge SMP and NUMA configurations

From: Oberman, Laurence (HAS GSE)
Date: Fri Oct 14 2011 - 12:53:21 EST

Standard RHEL kernel build.
What the customer would be using.

[root@linuxbeast boot]# cat config-2.6.32-131.6.1.el6.x86_64 | grep NR
CONFIG_NR_CPUS=4096

-----Original Message-----
From: Eric Dumazet [mailto:eric.dumazet@xxxxxxxxx]
Sent: Friday, October 14, 2011 12:40 PM
To: Oberman, Laurence (HAS GSE)
Cc: Seger, Mark; linux-kernel@xxxxxxxxxxxxxxx; Cabaniols, Sebastien
Subject: RE: Regression in reading /proc/stat in the newer kernels with large SMP and NUMA configurations

Le vendredi 14 octobre 2011 Ã 17:27 +0100, Oberman, Laurence (HAS GSE) a
Ãcrit :
> Eric,
>
> Got the system ready and ran the tests.
>
> This is a DL980 128 CPCUS, 256GB memory.
>
> [root@linuxbeast ~]# cat /proc/cpuinfo | grep processor | wc -l
> 128
>
> [root@linuxbeast ~]# uname -a
> Linux linuxbeast.gse.mvlabs.corp.hp.com 2.6.32-131.6.1.el6.x86_64 #1 SMP Mon Jun 20 14:15:38 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
>
> In this example we take >4ms per read. We are spending most of the time in
>
> 35.09% t [kernel.kallsyms] [k] kstat_irqs_cpu
> 32.13% t [kernel.kallsyms] [k] find_next_bit
> 24.32% t [kernel.kallsyms] [k] show_stat
> 1.98% t [kernel.kallsyms] [k] vsnprintf
> 1.63% t [kernel.kallsyms] [k] format_decode
> 1.23% t [kernel.kallsyms] [k] number

Hmm, have you compiled your kernel with NR_CPUS=4096 ???

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