From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: john stultz <johnstul@us.ibm.com>,
tglx@linutronix.de, linux-kernel@vger.kernel.org
Subject: Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards.
Date: Thu, 20 Oct 2005 10:01:07 +0200 [thread overview]
Message-ID: <20051020080107.GA31342@elte.hu> (raw)
In-Reply-To: <Pine.LNX.4.58.0510200340110.27683@localhost.localdomain>
* Steven Rostedt <rostedt@goodmis.org> wrote:
> > i could imagine the following hardware effects to cause time warps:
> >
> > - the TSC is in fact the 'read counter' method of the local APIC timer
> > hardware. So there can be interactions in theory: programming the APIC
> > timer could impact the TSC and vice versa. There have been CPU
> > erratums in this area in the past.
>
> Could this cause a 2 second drop backwards?
i dont think so.
> > - the TSC itself could have short, temporary warps. I had a box that
> > showed such effects.
>
> Can this be a 2 second warp?
the ones i saw were in the 1000-cycles range.
> My older code first used jiffies as a timer, then I switched to TSC
> and then to APIC timer, and then finally ktimer. ktimer was the first
> to show a backwards get_time.
another thing: the monotonicity check is only in get_ktime_mono(), while
there are other places where a monotonic clock is used, which this check
might miss.
Ingo
next prev parent reply other threads:[~2005-10-20 8:01 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-19 14:59 Ktimer / -rt9 (+custom) monotonic_clock going backwards Steven Rostedt
2005-10-19 15:10 ` Thomas Gleixner
2005-10-19 18:39 ` john stultz
2005-10-20 6:55 ` Steven Rostedt
2005-10-20 7:34 ` Ingo Molnar
2005-10-20 7:46 ` Steven Rostedt
2005-10-20 8:01 ` Ingo Molnar [this message]
2005-10-20 8:56 ` Steven Rostedt
2005-10-20 8:59 ` Ingo Molnar
2005-10-20 9:04 ` Steven Rostedt
2005-10-20 9:05 ` Steven Rostedt
2005-10-20 10:05 ` Steven Rostedt
2005-10-20 10:05 ` Steven Rostedt
2005-10-20 15:55 ` Ingo Molnar
2005-10-20 16:09 ` Steven Rostedt
2005-10-20 16:45 ` john stultz
2005-10-20 16:58 ` Steven Rostedt
2005-10-20 17:05 ` john stultz
2005-10-20 19:32 ` Ingo Molnar
2005-10-20 20:05 ` john stultz
2005-10-20 20:54 ` Ingo Molnar
2005-10-21 6:03 ` Steven Rostedt
2005-10-21 7:49 ` Thomas Gleixner
2005-10-21 7:57 ` Steven Rostedt
2005-10-21 8:00 ` ktimer API Steven Rostedt
2005-10-21 8:09 ` Thomas Gleixner
2005-10-21 18:09 ` Ktimer / -rt9 (+custom) monotonic_clock going backwards john stultz
2005-10-21 18:15 ` Thomas Gleixner
2005-10-20 22:06 ` George Anzinger
2005-10-20 6:19 ` Steven Rostedt
2005-10-20 14:34 ` Steven Rostedt
2005-10-20 15:18 ` Steven Rostedt
2005-10-20 15:23 ` Steven Rostedt
2005-10-20 16:01 ` Steven Rostedt
2005-10-19 15:11 ` Ingo Molnar
2005-10-20 6:38 ` Steven Rostedt
2005-10-20 6:56 ` Ingo Molnar
2005-10-19 15:21 ` Daniel Walker
2005-10-20 6:39 ` Steven Rostedt
2005-10-20 15:02 ` Daniel Walker
2005-10-20 22:19 ` George Anzinger
2005-10-20 23:23 ` john stultz
2005-10-19 16:44 ` Frank Sorenson
2005-10-20 6:43 ` Steven Rostedt
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