From: Stephen Hemminger <shemminger@osdl.org>
To: Joe Korty <joe.korty@ccur.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: gettimeofday resolution seriously degraded in test9
Date: Mon, 27 Oct 2003 16:15:02 -0800 [thread overview]
Message-ID: <20031027161502.3f98c556.shemminger@osdl.org> (raw)
In-Reply-To: <20031027234447.GA7417@rudolph.ccur.com>
On Mon, 27 Oct 2003 18:44:47 -0500
Joe Korty <joe.korty@ccur.com> wrote:
> [ 2nd posting, the first seems to have been lost ]
>
> Linus,
> This bit of -test9 code reduces the resolution of gettimeofday(2) from
> 1 microsecond to 1 millisecond whenever a negative time adjustment is
> in progress. This seriously damages efforts to measure time intervals
> accurately with gettimeofday. Please consider backing it out.
>
> Joe
The problem is that it is worse to have time go backwards which is what we
have done up until test9. It might be possible to compress time when NTP is doing
negative adjustments, but if you really care about microsecond resolution then
you will still lose.
If you care about microseconds, then NTP is going to whack your data. It has to
cause clock to speed up/slow down. Your data points will skip and stall due to it.
Use a different clock source or don't run NTP if you are doing real time stuff.
next prev parent reply other threads:[~2003-10-28 0:14 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-27 23:44 gettimeofday resolution seriously degraded in test9 Joe Korty
2003-10-28 0:15 ` Stephen Hemminger [this message]
2003-10-28 0:29 ` john stultz
2003-10-28 1:17 ` Stephen Hemminger
2003-10-28 11:55 ` Gabriel Paubert
2003-10-28 18:21 ` Stephen Hemminger
2003-10-29 10:07 ` Gabriel Paubert
2003-10-29 19:38 ` Stephen Hemminger
2003-10-29 22:50 ` Peter Chubb
2003-10-30 21:33 ` George Anzinger
2003-10-30 21:52 ` Richard B. Johnson
2003-10-30 22:50 ` Chris Friesen
2003-10-30 23:15 ` Peter Chubb
2003-10-30 23:47 ` George Anzinger
2003-11-25 16:42 ` [RFC] possible erronous use of tick_usec in do_gettimeofday Joe Korty
2003-11-25 17:13 ` Stephen Hemminger
2003-11-25 19:57 ` George Anzinger
2003-11-25 21:12 ` Joe Korty
2003-11-25 23:26 ` George Anzinger
2003-10-30 23:27 ` gettimeofday resolution seriously degraded in test9 George Anzinger
2003-10-30 10:39 ` Gabriel Paubert
[not found] <LphK.2Dl.15@gated-at.bofh.it>
[not found] ` <Lq47.3Go.11@gated-at.bofh.it>
[not found] ` <LqGL.4zF.11@gated-at.bofh.it>
[not found] ` <LAPN.1dU.11@gated-at.bofh.it>
[not found] ` <LGLz.1h2.5@gated-at.bofh.it>
2003-10-28 19:19 ` David Mosberger-Tang
2003-10-28 19:59 ` Stephen Hemminger
2003-10-29 0:19 ` David Mosberger
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