Re: [Qemu-devel] Qemu Trace

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Fri, Feb 02, 2018 at 03:53:45PM +0000, Peter Maydell wrote:
> On 2 February 2018 at 10:08, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > On Thu, Feb 01, 2018 at 04:30:10PM +0100, Nesrine Zouari wrote:
> >> I am a computer engineering student and I am actually working on my
> >> graduation project at Lauterbach company. The project is about Qemu Trace
> >> and as a future I would like to contribute this work to the main line.
> >>
> >> My project is divided into two parts:
> >>
> >> 1/ Collecting the Guest trace data : The trace solution should be able to
> >> provide:
> >>
> >>             a/ Instruction flow Trace
> >>
> >>             b/ Memory read/write access
> >>
> >>             c/ Time Stamps.
> >>
> >>             d/ For tracing rich operating systems that are using MMU, we
> >> additionally need to trace the task switches.
> >
> > Lluìs has done the most instrumentation work in qemu.git and can explain
> > the current status.
> 
> I think at the moment the status is that we're still discussing
> what the trace plugin API should be... there are some mailing

s/trace plugin API/instrumentation plugin API/

> list threads on the subject from I think last year some time.

The point of the instrumentation plugin API is for online analysis
(stuff that cannot be post-processed offline) with the ability for the
plugin to control QEMU (e.g. affect translation during a run).  That is
not necessary for Nesrine's use case.

I see two main requirements in Nesrine's use case:

1. Instruction flow, memory access, and task switch trace.  This doesn't
exist today and requires adding new trace events.

2. An external interface for processing traces.  There seems to be a
requirement for doing it online and not by post-processing trace files.
Therefore I suggested looking into LTTng UST, which has an efficient
interface and libraries for tracing processes.  I think no QEMU changes
are necessary here.

Stefan

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