From: Karim Yaghmour <karym@opersys.com>
To: Gabriel Paubert <paubert@iram.es>
Cc: Samuel Rydh <samuel@ibrium.se>,
linuxppc-dev@lists.linuxppc.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH] gettimeofday stability
Date: Wed, 11 Apr 2001 16:09:11 -0400 [thread overview]
Message-ID: <3AD4B9E7.C96F1088@opersys.com> (raw)
In-Reply-To: Pine.HPX.4.10.10104112111330.1891-100000@gra-ux1.iram.es
Gabriel Paubert wrote:
>
> Finally, if you _really_ run into this problem, given the delay between
> the decrementer interrupt and the update of tb_last_stamp, it means that
> you likely introduce uncertainties of several microseconds. I forgot also
> to mention that, to complicate matters, you have to check CPU type before
> you touch the TB (601 versus all others).
>
While porting the Linux Trace Toolkit to PPC I noticed a problem
that may be explained by the symptoms described. The way it works
is that LTT uses do_gettimeofday() to stamp the events that occur.
Occasionnaly, a trace would contain entries where the timestamp
will jump (from one event to the next) of approximately 4295 seconds.
Later on, this would come back to a "normal" value. And the
4295 seconds are 2^32/1000000. Hence the underflow.
This has been noticed with both 2.2.x and 2.4.x kernels.
===================================================
Karim Yaghmour
karym@opersys.com
Embedded and Real-Time Linux Expert
===================================================
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2001-04-11 20:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-04-11 19:00 [PATCH] gettimeofday stability Samuel Rydh
2001-04-11 19:42 ` Gabriel Paubert
2001-04-11 20:09 ` Karim Yaghmour [this message]
2001-04-11 21:31 ` Benjamin Herrenschmidt
2001-04-12 18:09 ` Gabriel Paubert
2001-04-14 6:49 ` Karim Yaghmour
2001-04-16 11:56 ` Gabriel Paubert
2001-04-16 13:25 ` Benjamin Herrenschmidt
2001-04-16 12:53 ` Gabriel Paubert
2001-04-17 11:22 ` Gabriel Paubert
2001-04-11 23:07 ` Samuel Rydh
2001-04-16 11:25 ` Gabriel Paubert
2001-04-19 20:43 ` Samuel Rydh
2001-04-21 15:21 ` Gabriel Paubert
2001-04-21 18:16 ` Samuel Rydh
2001-04-21 19:37 ` Gabriel Paubert
-- strict thread matches above, loose matches on Subject: below --
2001-04-16 16:00 Iain Sandoe
2001-04-16 22:19 ` Dan Malek
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