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

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Message-ID: <8DC664164FA4D1449479E7B36CDCFB1F221F0608B2@GVW0676EXC.americas.hpqcorp.net>
Date:	Fri, 14 Oct 2011 14:48:15 +0100
From:	"Oberman, Laurence (HAS GSE)" <Laurence.Oberman@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"Seger, Mark" <mark.seger@...com>
CC:	"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

Hi Eric,
I am preparing for that test. Need to stage a full RHEL6. I had only updated the kernel on an existing SLES10.
Standby and I will run the tests for you.

Thanks
Laurence

-----Original Message-----
From: Eric Dumazet [mailto:eric.dumazet@...il.com] 
Sent: Friday, October 14, 2011 9:47 AM
To: Seger, Mark
Cc: Oberman, Laurence (HAS GSE); 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 14:36 +0100, Seger, Mark a écrit :

> For me the easiest reproducer, which admittedly doesn't show any
> deeper analysis, is to just run "cat /proc/stat>/dev/null" in a loop
> and time it.

OK, but you already provided a global number.

We would like to check where in kernel cpu time is consumed.
Maybe something really obvious could pop out.

"perf" is provided in kernel sources, and really is a piece of cake.

cd tools/perf ; make 



2x4x2 means : Two sockets, 4 cores per physical package, 2 threads per
core.