linux-kernel - Re: Negative values in /proc/latency

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Message-ID: <20090203215552.38193470@infradead.org>
Date:	Tue, 3 Feb 2009 21:55:52 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Corrado Zoccolo <czoccolo@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Negative values in /proc/latency_stats

On Tue, 3 Feb 2009 21:46:09 -0800

> > + * (note: the average latency is the acummulated latency deviced
> > by the number
> > + * of times)
> 
> I was surprised at this.  Is the stack backtracer sufficiently
> reliable/repeatable for this to work?

yep it is, at least on x86 and x86-64.

> 
> > + * Negative latencies (caused by time going backwards) are also
> > explicitly
> > + * skipped.
> 
> Are we sure that this was the cause of the problem?

not 100%, but if you add only positive numbers..... the only other
option is an overflow.. but that would be such a huge latency that that
is not very believable.

> 
> Which time source is the caller using here, and why is it going
> backwards?

scheduler clock.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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