From: Philippe Gerum <rpm@xenomai.org>
To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: xenomai-core <xenomai@xenomai.org>
Subject: Re: [Xenomai-core] official TSC model on SMP
Date: Sun, 17 Sep 2006 19:15:28 +0200 [thread overview]
Message-ID: <1158513328.4979.45.camel@domain.hid> (raw)
In-Reply-To: <450D3764.80601@domain.hid>
On Sun, 2006-09-17 at 13:54 +0200, Jan Kiszka wrote:
> Hi,
>
> reading through timer code of Xenomai I just wondered (again) what our
> official model of TSCs on multiprocessor boxes are:
>
> 1) (practically) perfectly synchronised without offset
>
> 2) synchronised but with (unknown?) offset
>
> 3) unsynchronised
The current model is unsynchronized. If anything from the codebase is
found relying on the opposite, be it partially or fully, then it's
utterly broken in the SMP case, and I'm likely the one to blame.
IOW, we don't currently provide any guarantee to anyone that a timestamp
could be interpreted anywhere else than the CPU it was read from, and
leave all the related burden to the application developer (e.g. by mean
of managing CPU affinity constraints and the like).
>
> I'm asking because I worried about timestamps taken on external events
> like interrupts on one CPU and are then used to trigger some timed
> operation on another. Such things may easily happen via RTDM devices
> where we do not communicate the CPU source of event timestamps. But
> there is also other code influenced by the TSC model, e.g. data
> collection and evaluation for CPU load stats.
>
> Jan
>
> _______________________________________________
> Xenomai-core mailing list
> Xenomai-core@domain.hid
> https://mail.gna.org/listinfo/xenomai-core
--
Philippe.
next prev parent reply other threads:[~2006-09-17 17:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-17 11:54 [Xenomai-core] official TSC model on SMP Jan Kiszka
2006-09-17 17:15 ` Philippe Gerum [this message]
2006-09-17 17:36 ` Gilles Chanteperdrix
2006-09-18 9:43 ` Jan Kiszka
2006-09-19 21:46 ` Philippe Gerum
2006-09-20 8:17 ` Philippe Gerum
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1158513328.4979.45.camel@domain.hid \
--to=rpm@xenomai.org \
--cc=jan.kiszka@domain.hid \
--cc=xenomai@xenomai.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.