linux-kernel - Re: [PATCH 02/14] perf trace: Apply new perf_mmap__read

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Date:   Mon, 5 Mar 2018 10:46:52 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     kan.liang@...ux.intel.com, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org, namhyung@...nel.org,
        wangnan0@...wei.com, ak@...ux.intel.com
Subject: Re: [PATCH 02/14] perf trace: Apply new perf_mmap__read_event()
 interface

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@...ux.intel.com wrote:
> > > From: Kan Liang <kan.liang@...ux.intel.com>
> > > 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()?

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