On Wed, Aug 10, 2016 at 04:33:47PM +0200, Lluís Vilanova wrote: > Daniel P Berrange writes: > > > Describe use of per-subdir trace events files and how it impacts > > code generation. > > > Signed-off-by: Daniel P. Berrange <berra...@redhat.com> > > --- > > docs/tracing.txt | 61 > > +++++++++++++++++++++++++++++++++++++++++++++++--------- > > 1 file changed, 52 insertions(+), 9 deletions(-) > > > diff --git a/docs/tracing.txt b/docs/tracing.txt > > index 29f2f9a..b7ba179 100644 > > --- a/docs/tracing.txt > > +++ b/docs/tracing.txt > > @@ -27,18 +27,51 @@ for debugging, profiling, and observing execution. > > > == Trace events == > > > +=== Sub-directory setup === > > + > > Each directory in the source tree can declare a set of static trace events > > -in a "trace-events" file. Each trace event declaration names the event, its > > -arguments, and the format string which can be used for pretty-printing: > > +in a "trace-events" file. The first (non-comment) statement in the file > > +must be "@id_offset(NN)" where NN is an integer that is unique among all > > +"trace-events" files in the QEMU source tree. The IDs can be arbitrarily > > +chosen, but extra fun the current "trace-events" files use values from the > > +"powerful number" integer sequence :-) > > Can we get rid of the "@id_offset(NN)"? If we're generating a trace-events-all > all the same, we can use that to generate all the per-directory file *and* > still > keep the simpler flat event ids.
One thing that occurred to me is that we could take a hash of the group name. Since we have few enough sub-dirs / groups, and a large enough ID space, it ought to be possible to get a hash which is unique. The trace tool can double check that all groups get a unique hash > For example, first we concatenate /trace-events, /io/trace-events and > /hw/usb/trace-events into /trace-events-all to produce: > > @group core > @dir / > # contents of /trace-events > @group io > @dir /io > # contents of /io/trace-events > @group hw_usb > @dir /hw/usb > # contents of /hw/usb/trace-events > > Then we can use /trace-events-all to generate all the per-directory trace.h > files while ensuring a perfectly flat event identifier space (a single > generated-events.c is used). > > This should minimize changes to tracing code and avoid further restrictions > (like the "top-level vcpu" one). That means when any individual trace file is changed, we re-generate the world, which is exactly what this series is designed to avoid. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
