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Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint contr


From: Richard W.M. Jones
Subject: Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event)
Date: Thu, 21 Oct 2010 08:38:38 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Oct 21, 2010 at 07:20:27AM +0200, Christoph Hellwig wrote:
> On Tue, Oct 19, 2010 at 03:29:51PM +0100, Richard W.M. Jones wrote:
> > On Tue, Oct 19, 2010 at 03:59:36PM +0200, Jan Kiszka wrote:
> > > Once we have "-trace events=...", defining the list of active
> > > tracepoints before starting qemu will be trivial (e.g. via a config
> > > file). Of course, this requires that all tracepoints are built-in...
> > 
> > Sorry that I've not been following this very closely, but does this
> > sort of thing allow tracing reads and writes to block devices?  Am I
> > right in thinking that if a tracepoint existed in the right place, one
> > could get a log file from that which could be post-processed in
> > another tool?
> 
> I don't think it does.  But I have a patch that I need to update which
> outputs traces in the form of the Linux blktrace block I/O tracing tool,
> which does exactly what you need (and more).  You can simply use
> all the blktrace-enabled tools, including seekwatcher on it.

It's on the to-do list to use blktrace instead, so a patch
which changed qemu to produce blktrace-like output would
be useful.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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