From: george anzinger <george@mvista.com>
To: Tim Schmielau <tim@physik3.uni-rostock.de>
Cc: Patrick Moor <pmoor@netpeople.ch>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: time jumps (again)
Date: Mon, 04 Aug 2003 15:38:11 -0700 [thread overview]
Message-ID: <3F2EE053.1020600@mvista.com> (raw)
In-Reply-To: <Pine.LNX.4.33.0308042347300.12309-100000@gans.physik3.uni-rostock.de>
Tim Schmielau wrote:
>>Some days ago I started noticing strange time jumps on my Athlon system.
>>(Asus board, VIA chipset, AMD Athlon 650MHz processor). I haven't
>>noticed them before and I am pretty sure there weren't any for the last
>>few years! Uptime of the machine is now 218 days, and problems began
>>appearing after 215 days approximately.
>>
>>What happens: when doing a
>> $ while true; do date; done
>>I'm noticing time jumps _exactly_ at the beginning of a "new" second (or
>>at the end of an "old" one). the jump is exactly 4294 (4295) seconds
>>into the future. Example:
>>...
>>Mon Aug 4 18:11:06 CEST 2003
>>Mon Aug 4 18:11:06 CEST 2003
>>Mon Aug 4 19:22:41 CEST 2003
>>Mon Aug 4 19:22:41 CEST 2003
>>Mon Aug 4 19:22:41 CEST 2003
>>Mon Aug 4 18:11:07 CEST 2003
>>Mon Aug 4 18:11:07 CEST 2003
>>...
>>
>
>
> Wild guess - does the following patch fix it?
And your theory is that wall_jiffies > jiffies. How does this happen?
Both of these are only changed under the write_irq lock....
I would feel better with a patch that made jiffies volatile, but it
already is.
I agree that the jump implies overflow here, but just HOW is it happening?
Time for some dianostic code...
Tim
>
>
> --- linux-2.4.20/arch/i386/kernel/time.c.orig Mon Aug 4 23:38:47 2003
> +++ linux-2.4.20/arch/i386/kernel/time.c Mon Aug 4 23:40:53 2003
> @@ -274,8 +274,8 @@
> read_lock_irqsave(&xtime_lock, flags);
> usec = do_gettimeoffset();
> {
> - unsigned long lost = jiffies - wall_jiffies;
> - if (lost)
> + long lost = jiffies - wall_jiffies;
> + if (lost>0)
> usec += lost * (1000000 / HZ);
> }
> sec = xtime.tv_sec;
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> Please read the FAQ at http://www.tux.org/lkml/
>
--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml
next prev parent reply other threads:[~2003-08-04 22:38 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-04 16:35 time jumps (again) Patrick Moor
2003-08-04 16:37 ` Alan Cox
2003-08-04 21:49 ` Tim Schmielau
2003-08-04 22:38 ` george anzinger [this message]
2003-08-05 1:08 ` Andries Brouwer
2003-08-06 18:16 ` Timothy Miller
2003-08-06 18:55 ` George Anzinger
2003-08-07 0:29 ` Andries Brouwer
2003-08-05 10:32 ` Jan Niehusmann
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