From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Gabriel Paubert <paubert@iram.es>
Cc: linuxppc-dev list <linuxppc-dev@lists.linuxppc.org>,
Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: Time precision, adjtime(x) vs. gettimeofday
Date: Wed, 08 Oct 2003 18:22:58 +0200 [thread overview]
Message-ID: <1065630178.26943.54.camel@gaston> (raw)
In-Reply-To: <20031008154846.GA29868@iram.es>
> Well, it it affects gettimeofday which has a precision of 1 part in
> 10000 (100 ppm), it means that our boot time timebase calibration was
> not very good to start with, on my set of running VME machines I have
> the following (values in ppm):
>
> ../..
Boot time calibration can't be perfect... I depends very much on the
quality of what your are calibrating against, and the bus path to it.
On most pmacs, I'm calibrating either against a VIA timer which isn't
_that_ good or on OF value (which are themselves calibrated, I think,
against the KeyLargo timer).
On all cases, those will drift some way from what the NTP server will
give, either a lot or not, it will. So we may end up adjusting our
kernel rate and thus opening a window for the problem.
Ben.
next prev parent reply other threads:[~2003-10-08 16:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-08 13:32 Time precision, adjtime(x) vs. gettimeofday Benjamin Herrenschmidt
2003-10-08 15:48 ` Gabriel Paubert
2003-10-08 16:22 ` Benjamin Herrenschmidt [this message]
2003-10-08 17:50 ` Gabriel Paubert
2003-10-08 18:22 ` Benjamin Herrenschmidt
2003-10-08 18:25 ` [PATCH] " Stephen Hemminger
2003-10-08 18:43 ` Benjamin Herrenschmidt
2003-10-08 19:11 ` john stultz
2003-10-08 22:17 ` Pavel Machek
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