From: Andi Kleen <ak@muc.de>
To: jim.houston@attbi.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: LTP - gettimeofday02 FAIL
Date: 19 Nov 2002 13:03:48 +0100 [thread overview]
Message-ID: <m3bs4l7om3.fsf@averell.firstfloor.org> (raw)
In-Reply-To: <200211190127.gAJ1RWg11023@linux.local>
Jim Houston <jim.houston@attbi.com> writes:
> I believe that this is the result of lost ticks. It has gotten much
> easier to lose a tick since HZ was changed to 1000. When the timer
> interrupt is delayed, the other processors will continue to keep reasonable
> time (based on the TSC), but when the timer interrupt eventually happens,
> it will add one tick's worth of nanoseconds to xtime.tv_nsec and set
> last_tsc_low to the current tsc value. The other processors now base
> their time on this new last_tsc_low and will see time go backwards.
It could be detected by keeping a per cpu last_tsc.
Best would be to use a global timer like HPET, but it's not available
everywhere and much slower than rdtsc too.
-Andi
next prev parent reply other threads:[~2002-11-19 11:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-19 1:27 LTP - gettimeofday02 FAIL Jim Houston
2002-11-19 12:03 ` Andi Kleen [this message]
2002-11-19 13:37 ` [LTP] " Paul Larson
2002-11-19 14:02 ` Dave Jones
2002-11-19 14:50 ` Paul Larson
-- strict thread matches above, loose matches on Subject: below --
2002-11-12 22:11 Paul Larson
2002-11-14 21:52 ` Chris Wedgwood
2002-11-18 17:34 ` Paul Larson
2002-11-18 21:58 ` Chris Wedgwood
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