Subject: Re: [PULL] hardware latency detector
From: Jon Masters <jonathan@jonmasters.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jon Masters <jcm@jonmasters.org>, mingo@elte.hu, tglx@linutronix.de,
       williams@redhat.com, linux-kernel@vger.kernel.org
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	 <alpine.LFD.2.01.0906181824540.16802@localhost.localdomain>
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Organization: World Organi[sz]ation Of Broken Dreams
Date: Thu, 18 Jun 2009 21:32:20 -0400
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On Thu, 2009-06-18 at 18:25 -0700, Linus Torvalds wrote:
> 
> On Thu, 18 Jun 2009, Jon Masters wrote:
> > 
> > Please pull "hwlat", the hardware latency detector for 2.6.31.
> 
> I really want to know more before I pull.

Ok.

> Has this been in -next?

No, it hasn't. But it has been tested quite extensively by a number of
people and is currently in the -rt tree.

> Discussed on lkml?

Yes. I posted an RFC patch back when it was called the SMI detector,
then a patch last week with the new generic name of hardware latency
detector (at Ingo's suggestion of renaming).

> How does it work?

It started as an SMI detector. Basically, when this module is loaded and
enabled, it will grab all CPUs in periodic calls to stop_machine and sit
in a configurable loop, looking for unexplainable latencies. Doing it
this way allows us to look for something stealing the CPU from Linux
without the kernel knowing - we report the statistics via debugfs.

Hope that helps! Thanks Linus!

Jon.


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