Re: [Qemu-devel] [PATCH 00/14] trace: Add static tracing to QEMU

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/12/2010 05:36 AM, Stefan Hajnoczi wrote:
> This patch series adds static tracing to QEMU.  It can be used to instrument
> QEMU code by means of lightweight logging called trace events.
>
> Prerna and I are now posting the entire patch series with a serious eye towards
> checking we meet users' and developers' tracing needs and with the goal of
> getting this functionality merged into qemu.git.
>
> Tracing infrastructure allows debugging, performance analysis, and observation
> to be performed.  Right now there are ad-hoc logging calls in some source files
> which require rebuilding QEMU with certain #defines and perform poorly.  This
> patch series introduces a single tracing infrastructure which is easy to use
> and can replace ad-hoc techniques.
>
> Two key points:
>
> 1. The trace-events file contains the set of defined trace events which can be
>     called from a source file.  For example, trace-events has:
>
>      qemu_malloc(size_t size, void *ptr) "size %zu ptr %p"
>
>     and qemu-malloc.c uses this trace event like this:
>
>      #include "trace.h"  /* needed for trace event prototype */
>
>      void *qemu_malloc(size_t size)
>      {
>          void *ptr;
>          if (!size&&  !allow_zero_malloc()) {
>              abort();
>          }
>          ptr = oom_check(malloc(size ? size : 1));
>          trace_qemu_malloc(size, ptr);  /*<-- trace event */
>          return ptr;
>      }
>
> 2. The built-in 'simple' trace backend writes binary traces to
>     /tmp/trace-<pid>.  They can be pretty-printed like this:
>
>      ./simpletrace.py trace-events /tmp/trace-*
>
>     Although you can also try LTTng Userspace Tracer ('ust' trace backend), the
>     'simple' trace backend provides commands within the QEMU monitor to
>     enable/disable trace events at runtime.  It is easy to use and should serve
>     as a good default trace backend.
>
>     The 'simple' trace backend's limitation is that it isn't thread-safe and can
>     therefore only trace correctly when the QEMU global mutex is held.
>
> For full documentation, see:
> http://repo.or.cz/w/qemu/stefanha.git/blob_plain/8d9f8f62d5af986fab6636770450f57fbd0d8b66:/docs/tracing.txt
>
> The git branch is here:
> http://repo.or.cz/w/qemu/stefanha.git/shortlog/refs/heads/tracing
>    

This turned out very nice.  Good work!

Regards,

Anthony Liguori

> Stefan
>
>
>
>