linux-kernel - Re: gettimeofday() jumping into the future

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Message-Id: <1206979407.6175.2.camel@jstultz-laptop>
Date:	Mon, 31 Mar 2008 09:03:27 -0700
From:	John Stultz <johnstul@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Tim Ricketts <tr@...th.li>, Michael Smith <msmith@...h.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Wingo <wingo@...endo.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: gettimeofday() jumping into the future


On Mon, 2008-03-31 at 10:55 +0200, Thomas Gleixner wrote:
> 
> > +     if (cycle_now < clock->cycle_last)
> > +             return 0;
> > +
> 
> No, this breaks wrapping clocksources e.g. pmtimer. We need a
> different sanity check for that TSC crap.

Yea. If you're going to do that sort of logic (which requires a costly
cmpxchg as well), it should be done in the read() function of the
clocksource.

thanks
-john
 

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