linux-kernel - RE: Regression in reading /proc/stat in the newer kernels with large SMP and NUMA configurations

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Date:	Fri, 14 Oct 2011 17:52:31 +0100
From:	"Oberman, Laurence (HAS GSE)" <Laurence.Oberman@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"Seger, Mark" <mark.seger@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Cabaniols, Sebastien" <Sebastien.Cabaniols@...com>
Subject: RE: Regression in reading /proc/stat in the newer kernels with
 large SMP and NUMA configurations

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

[root@...uxbeast 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@...il.com] 
Sent: Friday, October 14, 2011 12:40 PM
To: Oberman, Laurence (HAS GSE)
Cc: Seger, Mark; linux-kernel@...r.kernel.org; Cabaniols, Sebastien
Subject: RE: Regression in reading /proc/stat in the newer kernels with large SMP and NUMA configurations

Le vendredi 14 octobre 2011 à 17:27 +0100, Oberman, Laurence (HAS GSE) a
écrit :
> Eric,
> 
> Got the system ready and ran the tests.
> 
> This is a DL980 128 CPCUS, 256GB memory.
> 
> [root@...uxbeast ~]# cat /proc/cpuinfo | grep processor | wc -l
> 128
> 
> [root@...uxbeast ~]# 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 ???