lkml.org 
[lkml]   [2002]   [Dec]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectHow much we can trust packet timestamping
From
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
-----------------------------------------------------------------------------
"Computers are useless. They can only give answers." Pablo Picasso
---> Visita http://www.valux.org/ para saber acerca de la <---
---> Asociación Valenciana de Usuarios de Linux <---
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2005-03-22 13:32    [from the cache]
©2003-2011 Jasper Spaans