[Qemu-devel] Re: [PATCH 03/10] Add printf debug to savevm

[Juan Quintela <quintela@redhat.com>]

Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> wrote:
> On Mon, Nov 29, 2010 at 08:00:18PM -0600, Anthony Liguori wrote:
>> Yeah, all of this should be done via tracing.  Maybe Stefan can make
>> some suggestions.
>
> Here is an example of how to record savevm timestamps using tracing.
> Actually the timestamp is recorded automatically when a trace event
> fires.
>
> Add these to the trace-events file:
> savevm_start(void) ""
> savevm_stop(unsigned int section_id) "section_id %u"
>
> Then use trace_savevm_start() instead of START_SAVEVM_CLOCK() and
> trace_savevm_stop() instead of STOP_SAVEVM_CLOCK() in savevm.c.  Also
> #include "trace.h".
>
> All the macros and inline timestamp analysis can be removed from
> savevm.c.
>
> ./configure --trace-backend=simple [...]
> make
>
> After running savevm look for the trace-<pid> file that QEMU produces in
> its current working directory.  You can pretty-print it like this:
> ./simpletrace.py trace-events trace-<pid>
>
> The second field in the simpletrace.py output is the time delta (in
> microseconds) since the last trace event.  So you can easily see how
> long start->stop took.
>
> For more info see docs/tracing.txt.  You might prefer to use SystemTap
> (./configure --trace-backend=dtrace) so you can write stap scripts to do
> more powerful analysis.

Thanks.

Searching for guru, I basically want to only print the values when the
difference is bigger that some values (number of calls is really big, I
need to learn how to script the analisys).

But clearly this "have to be" easier than change printf's and ifs and
rerun the test.

Later, Juan.

> Stefan