linux-kernel - Re: 2.6.25.2 - Jiffies/Time jumping back and forth (Regereesion from 2.6.24)

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Message-Id: <1210186778.16386.5.camel@jstultz-laptop>
Date:	Wed, 07 May 2008 11:59:38 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Martin Knoblauch <spamtrap@...bisoft.de>
Cc:	linux-kernel@...r.kernel.org, Chris McDermott <lcm@...ibm.com>
Subject: Re: 2.6.25.2 - Jiffies/Time jumping back and forth (Regereesion
	from 2.6.24)

On Wed, 2008-05-07 at 11:14 -0700, Martin Knoblauch wrote:
> > The printk timestamps may jump around a bit at bootup,  especially if
> > you have unsynced TSCs, so that is a known issue. However its not
> > known to have any actual negative effect other then maybe causing the
> > dmesg log to be a bit confusing.
> > 
> 
>  the problem, is not just at bootup and the jumping. During the
> *complete* lifetime of the kernel I see:
> 
> a) the dmesg timestamps jumping back and forth
> b) the values are much to small and have absolutely no relation to
> "seconds after bootup", as they have with 2.6.24 and before.
> 
>  But you are right, it might not be a jiffie problem, but a "dmesg
> timestamp" thing.

Hrmm.. So the issue persisting over the lifetime of the kernel is a new
one by me. This may also have some effect in scheduling decisions (not
necessarily causing a correctness issue, but a performance one). Also it
may have some effect on thread cputime values.

Please do open a bug and provide example dmesg output. I'll try to tag
some folks who have access to the same system type. 

thanks
-john


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