Re: [PATCH 4/5] perf tools: Allow to ignore missing pid

[Arnaldo Carvalho de Melo]

Em Mon, Dec 12, 2016 at 11:32:09AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Dec 12, 2016 at 11:35:42AM +0100, Jiri Olsa escreveu:
> > Adding perf_evsel::ignore_missing_cpu_thread bool.
> > 
> > When set true, it allows perf to ignore error of missing
> > pid of perf event syscall.
> > 
> > We remove missing thread id from the thread_map, so the
> > rest of the processing like ioctl and mmap won't get
> > disturbed with -1 fd
> 
> What was the test performed? I tried it here the following while doing
> a 'make -j4 allmodconfig' in the background, i.e. tons of threads coming
> and going, and I sometimes get:
> 
> [root@jouet ~]# perf record -u acme 
> Error:
> The sys_perf_event_open() syscall returned with 3 (No such process) for
> event (cycles:ppp).
> /bin/dmesg may provide additional information.
> No CONFIG_PERF_EVENTS=y kernel support configured?
> [root@jouet ~]#

So I applied the first three patches, will continue after discussing
this.

- Arnaldo
  
> > The reason for supporting this is to ease up monitoring
> > group of pids, that 'disappear' before perf opens their
> > event. This currently leads perf to report error and exit
> > and makes perf record's -u option unusable under certain
> > setup.
> > 
> > With this change we will allow this race and ignore such
> > failure with following warning:
> > 
> >   WARNING: Ignored open failure for pid 8605
> > 
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > Cc: David Ahern <dsahern@xxxxxxxxx>
> > Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > Link: http://lkml.kernel.org/n/tip-atmzsjyhrt1j6xjwwmb84upg@xxxxxxxxxxxxxx
> > ---
> >  tools/perf/perf.h       |  1 +
> >  tools/perf/util/evsel.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
> >  tools/perf/util/evsel.h |  1 +
> >  3 files changed, 46 insertions(+)
> > 
> > diff --git a/tools/perf/perf.h b/tools/perf/perf.h
> > index 9a0236a4cf95..1c27d947c2fe 100644
> > --- a/tools/perf/perf.h
> > +++ b/tools/perf/perf.h
> > @@ -55,6 +55,7 @@ struct record_opts {
> >  	bool	     all_user;
> >  	bool	     tail_synthesize;
> >  	bool	     overwrite;
> > +	bool	     ignore_missing_thread;
> >  	unsigned int freq;
> >  	unsigned int mmap_pages;
> >  	unsigned int auxtrace_mmap_pages;
> > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > index fd61ebd77c26..ac87f1637ae9 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -990,6 +990,8 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts,
> >  	 * it overloads any global configuration.
> >  	 */
> >  	apply_config_terms(evsel, opts);
> > +
> > +	evsel->ignore_missing_thread = opts->ignore_missing_thread;
> >  }
> >  
> >  static int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)
> > @@ -1419,6 +1421,33 @@ static int __open_attr__fprintf(FILE *fp, const char *name, const char *val,
> >  	return fprintf(fp, "  %-32s %s\n", name, val);
> >  }
> >  
> > +static bool ignore_missing_thread(struct perf_evsel *evsel,
> > +				  struct thread_map *threads,
> > +				  int thread, int err)
> > +{
> > +	if (!evsel->ignore_missing_thread)
> > +		return false;
> > +
> > +	/* The system wide setup does not work with threads. */
> > +	if (!evsel->system_wide)
> > +		return false;
> > +
> > +	/* The -ESRCH is perf event syscall errno for pid's not found. */
> > +	if (err != -ESRCH)
> > +		return false;
> > +
> > +	/* If there's only one thread, let it fail. */
> > +	if (threads->nr == 1)
> > +		return false;
> > +
> > +	if (thread_map__remove(threads, thread))
> > +		return false;
> > +
> > +	pr_warning("WARNING: Ignored open failure for pid %d\n",
> > +		   thread_map__pid(threads, thread));
> > +	return true;
> > +}
> > +
> >  static int __perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,
> >  			      struct thread_map *threads)
> >  {
> > @@ -1491,6 +1520,21 @@ static int __perf_evsel__open(struct perf_evsel *evsel, struct cpu_map *cpus,
> >  
> >  			if (fd < 0) {
> >  				err = -errno;
> > +
> > +				if (ignore_missing_thread(evsel, threads, thread, err)) {
> > +					/*
> > +					 * We just removed 1 thread, so take a step
> > +					 * back on thread index and lower the upper
> > +					 * nthreads limit.
> > +					 */
> > +					nthreads--;
> > +					thread--;
> > +
> > +					/* ... and pretend like nothing have happened. */
> > +					err = 0;
> > +					continue;
> > +				}
> > +
> >  				pr_debug2("\nsys_perf_event_open failed, error %d\n",
> >  					  err);
> >  				goto try_fallback;
> > diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> > index 6abb89cd27f9..06ef6f29efa1 100644
> > --- a/tools/perf/util/evsel.h
> > +++ b/tools/perf/util/evsel.h
> > @@ -120,6 +120,7 @@ struct perf_evsel {
> >  	bool			tracking;
> >  	bool			per_pkg;
> >  	bool			precise_max;
> > +	bool			ignore_missing_thread;
> >  	/* parse modifier helper */
> >  	int			exclude_GH;
> >  	int			nr_members;
> > -- 
> > 2.7.4