Re: [PATCH 02/14] perf trace: Apply new perf_mmap__read_event() interface

[Liang, Kan]

On 3/5/2018 8:46 AM, Arnaldo Carvalho de Melo wrote:
> Em Mon, Mar 05, 2018 at 10:03:39AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Sat, Mar 03, 2018 at 12:30:22AM +0100, Jiri Olsa escreveu:
> > > On Thu, Mar 01, 2018 at 06:08:59PM -0500, kan.liang@xxxxxxxxxxxxxxx wrote:
> > > > From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > > > The perf trace still use the legacy interface.
> > > > +++ b/tools/perf/builtin-trace.c
> > > > @@ -2472,8 +2472,14 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
> > > >   
> > > >   	for (i = 0; i < evlist->nr_mmaps; i++) {
> > > >   		union perf_event *event;
> > > > +		struct perf_mmap *md;
> > > > +		u64 end, start;
> > > >   
> > > > -		while ((event = perf_evlist__mmap_read(evlist, i)) != NULL) {
> > > > +		md = &evlist->mmap[i];
> > > > +		if (perf_mmap__read_init(md, 0, &start, &end) < 0)
> > > > +			continue;
> > > > +
> > > > +		while ((event = perf_mmap__read_event(md, 0, &start, end)) != NULL) {
> > > >   			struct perf_sample sample;
> > > >   
> > > >   			++trace->nr_events;
> > > > @@ -2486,7 +2492,7 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
> > > >   
> > > >   			trace__handle_event(trace, event, &sample);
> > > >   next_event:
> > > > -			perf_evlist__mmap_consume(evlist, i);
> > > > +			perf_mmap__consume(md, 0);
> > >
> > > could you call this with 'false' instead of 0, it's 'bool overwrite'
> > > applies also to the rest of the patchset
> >
> > I'm doing this, the argument is 'bool', so the value should be false or
> > true, even '0' being way shorter...
>
> While doing that I wonder why is that we can't do it without those
> explicit start/end variables in all the call sites and passing
> overwrite, start and end as parameters...
>
> Can't we just add 'overwrite, 'start' and 'end' to struct perf_mmap,
> then have perf_mmap__read_init() with just 'md' and 'overwrite' as
> parameters, initialize md->{start,end} and set md->overwrite to the
> 'overwrite' parameter in 'perf_mmap__read_init()' and then use just
> md as parameters for both perf_mmap__read_event() and
> perf_mmap__consume()?

I don't see any reason we cannot do this.
I will do some test. If it works well, I will submit the follow-up patch 
to clean up the interface.

Thanks,
Kan

> What am I missing to have this much simpler without all this
> boilerplate?
>
> Anyway, finishing the s/0/false/g, will leave this for later, but please
> comment on it.
>
> - Arnaldo