linux-kernel - Re: [PATCH 1/1] rasd: Use perf_evlist_

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Date:	Tue, 7 Oct 2014 10:32:36 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Jean Pihet <jean.pihet@...aro.org>
Cc:	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fu Wei <fu.wei@...aro.org>, Robert Richter <rric@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/1] rasd: Use perf_evlist__open() instead of open coded

Em Tue, Oct 07, 2014 at 10:45:14AM +0200, Jean Pihet escreveu:
> > --- a/src/rasd.c
> > -       evlist__for_each(evlist, c) {
> > -               /* On all online cpus by default, system wide tracing */
> > -               if (perf_evsel__open(c, evlist->cpus, NULL) < 0)
> > -                       err("opening tracepoint, are you root?");
> > -       }
> > -       perf_evlist__set_id_pos(evlist);
> > +       /* On all online cpus by default, system wide tracing */
> > +       if (perf_evlist__open(evlist) < 0)
> > +               err("opening tracepoint, are you root?");
 
> That way the system wide tracing does not work. perf_evlist__open uses
> a non-NULL thread mapping and so it only traces the events generated
> by the daemon itself.
 
> perf top uses a similar approach but uses a lot of code in machine.c
> (machine__synthesize_threads) and util/event.c
> (perf_event__synthesize_threads) to synthesize the threads etc., which
> we want to avoid in the minimalistic approach of rasd.

Humm, I will look into making it support this usecase, the point of
evsel/evlist is to try to abstract away as much as possible, leaving
just a few methods to be used by tools.

I think the default for perf_evlist__open() should be the most useful
for the majority of tools, which I thought would serve rasd well. It is
not the case, so I'll into how the tools that currently use
perf_evlist__open() behave and try to get a sane default in place.

Hopefully we will completely remove the need to set up any thread or cpu
map, as what you want is syswide tracing, right?

- Arnaldo
 
> Maybe I missed something about the system wide tracing, any suggestion
> is welcome.
> 
> Thanks for looking!
> 
> Jean
> 
> >
> >         /* mmap buffers */
> >         if (perf_evlist__mmap(evlist, 4 /* opts->mmap_pages */, false) < 0)
> > --
> > 1.9.3
> >
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