linux-kernel - Re: Using sched_clock for mmio-trace

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Message-ID: <y0mr6sq2hfj.fsf@ton.toronto.redhat.com>
Date:	16 Feb 2007 11:30:56 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Jeff Muizelaar <jeff@...idigm.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Using sched_clock for mmio-trace

Jeff Muizelaar <jeff@...idigm.net> writes:

> I've built a tool with the goal of logging mmio writes and reads by
> device drivers. See http://nouveau.freedesktop.org/wiki/MmioTrace.

FWIW, this is exactly a type of add-on trace patch that could be
mooted by adoption of the ltt/systemtap "marker" facility.  With it,
you would not need so much code (e.g. no new user-space tools at all,
reuse of common tracing buffer logic, permanently placed hooks) and
would probably get more utility.

> [...]  The question is, what [timer] api should I be using? I need
> something that can be called from inside interrupt handlers, and
> obviously the more accurate and the lower the overhead the better.

We in systemtap land have the same problem, and so far made do with
slightly postprocessed per-cpu TSC values.

- FChE
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