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

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

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.

Stefan