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Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint contr
From: |
Daniel P. Berrange |
Subject: |
Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event) |
Date: |
Thu, 21 Oct 2010 09:51:50 +0100 |
User-agent: |
Mutt/1.4.1i |
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?
>
> cf:
> http://rwmj.wordpress.com/2010/10/05/visualizing-reads-writes-and-alignment/#content
While having a static tracepoint in the right place would be best, it
is not strictly neccessary with a tool like DTrace/SystemTAP. With the
qemu debuginfo available, those tools can dynamically insert a probe
into any QEMU function at any point in the code. So you could easily
replace your QEMU patch from that blog post with a simple trace script
and get the same info dynamically. The benefit of static markers is
that they can provide standard named probe point + args, which are
stable long term, even as the code is re-factored/renamed/moved, etc.
Regards,
Daniel
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- Re: [Qemu-devel] Re: Static tracepoint control via trace-event, (continued)
- Re: [Qemu-devel] Static tracepoint control via trace-event, Daniel P. Berrange, 2010/10/19
- Re: [Qemu-devel] Static tracepoint control via trace-event, Stefan Hajnoczi, 2010/10/19
- Re: [Qemu-devel] Static tracepoint control via trace-event, Jan Kiszka, 2010/10/19
- Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Richard W.M. Jones, 2010/10/19
- [Qemu-devel] Re: Tracing block devices, Jan Kiszka, 2010/10/19
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Stefan Hajnoczi, 2010/10/19
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Christoph Hellwig, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Richard W.M. Jones, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event), Stefan Hajnoczi, 2010/10/21
- Re: Tracing block devices (was: Re: [Qemu-devel] Static tracepoint control via trace-event),
Daniel P. Berrange <=