Message-ID: <446A53DE.6060400@de.ibm.com>
Date: Wed, 17 May 2006 00:36:14 +0200
From: Martin Peschke <mp3@de.ibm.com>
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To: Andrew Morton <akpm@osdl.org>
CC: linux-kernel@vger.kernel.org, ak@suse.de, hch@infradead.org,
       arjan@infradead.org, James.Smart@Emulex.Com,
       James.Bottomley@SteelEye.com
Subject: Re: [RFC] [Patch 7/8] statistics infrastructure - exploitation prerequisite
References: <446A1023.6020108@de.ibm.com> <20060516112824.39b49563.akpm@osdl.org>
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Andrew Morton wrote:
> Martin Peschke <mp3@de.ibm.com> wrote:
>> need sched_clock for latency statistics
> 
> sched_clock() probably isn't suitable for this application.  It's a
> scheduler thing and has a number of accuracy problems.
> 
> But I thought we discussed this last time around?  Maybe not.

I have been too obsessed with the other issues to remember.

 > Maybe you've considered sched_clock()'s drawbacks and you've decided
 > they're all acceptable.

Admittedly, I didn't, but merely believed the comment above the function.

http://marc.theaimsgroup.com/?l=linux-kernel&m=114657675408686&w=2
sheds some light.

I would be happy to exploit an API that may result from that discussion.
I would plead for exporting such an API to modules. I don't see how
to implement statistics for latencies, otherwise.

Any other hints on how to replace my sched_clock() calls are welcome.
(I want to measure elapsed times in units that are understandable to
users without hardware manuals and calculator, such as milliseconds.)

Martin

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