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Re: [Qemu-devel] [PATCH 0/6] hypertrace: Lightweight guest-to-QEMU trace
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH 0/6] hypertrace: Lightweight guest-to-QEMU trace channel |
Date: |
Mon, 29 Aug 2016 09:45:02 -0400 |
User-agent: |
Mutt/1.6.2 (2016-07-01) |
On Wed, Aug 24, 2016 at 12:25:54PM +0200, Lluís Vilanova wrote:
> Stefan Hajnoczi writes:
>
> > On Sun, Aug 21, 2016 at 02:32:34PM +0200, Lluís Vilanova wrote:
> >> Unfortuntely, I've been unable to to make dtrace recognise QEMU's events
> >> (I'm
> >> only able to see the host kernel events). If someone with more experience
> >> on it
> >> can help me use dtrace with QEMU's events, I'll also add the supporting
> >> library
> >> to let dtrace do the callout to QEMU's moitor interface and control the
> >> events,
> >> and add a prperly useful example of that on the hypertrace docs (which was
> >> my
> >> original intention).
>
> > Which "dtrace" and host OS are you using?
>
> > QEMU builds with static user-space probes. You need to tell DTrace or
> > SystemTap to enable those probes in order to record trace data.
>
> I'm using debian on a 4.6.0-1-amd64 kernel with systemtap 3.0.6.
>
> I just gave it another try, and works if I use probes like:
>
> process("<binary-path>").mark("<event-name>")
>
> although they don't seem to appear on "stap -l" or anything like that (I
> cannot
> find a "qemu" provider). But I'm still unable to print the event values. This:
The following enumerates events for me:
$ sudo stap -L 'process("/usr/bin/qemu-system-x86_64").mark("*")'
process("/usr/bin/qemu-system-x86_64").mark("alsa_no_frames") $arg1:long
process("/usr/bin/qemu-system-x86_64").mark("alsa_pollout") $arg1:long
$arg2:long
process("/usr/bin/qemu-system-x86_64").mark("alsa_read_zero") $arg1:long
...
You can also use /usr/share/systemtap/tapset/qemu-system-x86_64.stp.
I'm running Fedora 24 with qemu-system-x86 2.6.0-5.fc24 and SystemTap
3.0-3.fc24.
> Also, I'm still not sure how to interact with QEMU's monitor interface from
> within the probe code (probes execute in kernel mode, including "guru mode"
> code).
When SystemTap is used the QEMU monitor interface does nothing.
Stefan
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