From: Arjan van de Ven <arjan@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Corrado Zoccolo <czoccolo@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Negative values in /proc/latency_stats
Date: Tue, 3 Feb 2009 21:55:52 -0800 [thread overview]
Message-ID: <20090203215552.38193470@infradead.org> (raw)
In-Reply-To: <20090203214609.39c9c6b2.akpm@linux-foundation.org>
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
For development, discussion and tips for power savings,
visit http://www.lesswatts.org
next prev parent reply other threads:[~2009-02-04 5:55 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-31 13:42 Negative values in /proc/latency_stats Corrado Zoccolo
2009-02-02 7:42 ` Harik
2009-02-03 4:55 ` Andrew Morton
2009-02-03 15:19 ` Arjan van de Ven
2009-02-04 0:16 ` Arjan van de Ven
2009-02-04 5:46 ` Andrew Morton
2009-02-04 5:55 ` Arjan van de Ven [this message]
2009-02-06 22:50 ` Corrado Zoccolo
2009-02-05 0:57 ` Tim Pepper
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