Re: [Xen-devel] [PATCH] tools: adds tracer on qemu-xen debug configure options

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Thu, Oct 10, 2013 at 09:52:16AM +0100, Ian Campbell wrote:
> On Thu, 2013-10-10 at 10:14 +0200, Fabio Fantoni wrote:
> > Il 03/10/2013 15:35, Fabio Fantoni ha scritto:
> > > Il 03/10/2013 15:08, Ian Campbell ha scritto:
> > >> On Fri, 2013-09-27 at 16:00 +0200, Fabio Fantoni wrote:
> > >>> When building tools in debug mode (debug=y), pass also
> > >>> --enable-trace-backend=stderr when configuring qemu-xen.
> > >>> Useful to improve debug.
> > >> What does this actually do in practice? More logging
> > >> in /var/log/xen/qemu-dm-$dom.log or something else?
> > >
> > > Yes, I think that stderr backend is good because the log will go on 
> > > /var/log/xen/qemu-dm-$dom.log (easy and fast).
> > > To use it must be configured with some qemu parameters, containing the 
> > > type of events to log. Setting it with "device_model_args" should be 
> > > sufficent instead adding other libxl option, and this should be used 
> > > only on some debug case.
> > > All details here:
> > > http://git.qemu.org/?p=qemu.git;a=blob;f=docs/tracing.txt
> > >
> > 
> > Any hints on this?
> 
> I missed Stefano's ack and was waiting for a qemu person to chime in,
> sorry.
> 
> There was some previous discussion about whether this kind tracing was
> the right solution:
> http://thread.gmane.org/gmane.comp.emulators.xen.devel/164858/focus=165379

The discussion was for a particular case, and was not about qemu trace
itself.

> I guess however that enabling this in our own debug builds of qemu (i.e.
> this patch) is OK, but long term something which can work for distro
> qemu builds would be better.

Having trace compiled in for debug purpose is a good idee, it make it
possible to enable some extra debug print without recompiling qemu. And
by default, they won't be any extra debug print in the logs.

So ACK to add --enable-trace... to a debug build.

-- 
Anthony PERARD

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