From: uaca@alumni.uv.es
To: linux-kernel@vger.kernel.org
Subject: How much we can trust packet timestamping
Date: Mon, 30 Dec 2002 12:28:38 +0100 [thread overview]
Message-ID: <20021230112838.GA928@pusa.informat.uv.es> (raw)
Hi all
IMHO The problem is quite complicated because
+ common hardware is not designed for real time:
- sends multiple PDUs within one interrupt, and can be delayed
- Host adapter bus & infraestructure is not designed to garantee latency
etc...
+ software is also not designed for realtime
- drivers may timestamp in softirq's
- irqs has no deterministic latency either
etc...
So even if do_gettimeofday() has 1/CPUfreq resolution by using TSC register
packet timestamping meassurement is biased, how much?
anybody has studied this? are there reports/doc about this topic?
of course, this can be avoided by using specialiced hardware, but I'm not
interested on that and I would like to know how much I can trust this
timestamps
Any comment would be greatly appreciated
Thanks
Ulisses
Debian GNU/Linux: a dream come true
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next reply other threads:[~2002-12-30 11:20 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-30 11:28 uaca [this message]
2002-12-30 13:09 ` How much we can trust packet timestamping Alan Cox
2002-12-30 13:01 ` uaca
2002-12-30 15:10 ` Alan Cox
2003-01-10 22:07 ` Werner Almesberger
2003-01-11 2:43 ` Alan Cox
2003-01-12 23:04 ` Werner Almesberger
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