linux-kernel - Re: [PATCH 34/40] perf report: Parallelize perf report using multi-thread

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Date:	Tue, 19 May 2015 23:58:22 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 34/40] perf report: Parallelize perf report using
 multi-thread

On Tue, May 19, 2015 at 12:12:30PM +0200, Jiri Olsa wrote:
> On Mon, May 18, 2015 at 09:30:49AM +0900, Namhyung Kim wrote:
> 
> SNIP
> 
> > +
> > +int perf_session__process_events_mt(struct perf_session *session, void *arg)
> > +{
> > +	struct perf_data_file *file = session->file;
> > +	struct perf_evlist *evlist = session->evlist;
> > +	struct perf_evsel *evsel;
> > +	u64 nr_entries = 0;
> > +	struct perf_tool *tool = session->tool;
> > +	struct perf_session *mt_sessions = NULL;
> > +	struct perf_tool_mt *mt_tools = NULL;
> > +	struct perf_session *ms;
> > +	struct perf_tool_mt *mt;
> > +	pthread_t *th_id;
> > +	int err, i, k;
> > +	int nr_index = session->header.nr_index;
> > +	u64 size = perf_data_file__size(file);
> > +
> 
> SNIP
> 
> > +
> > +	for (i = 1; i < nr_index; i++) {
> > +		mt = &mt_tools[i];
> > +
> > +		evlist__for_each(evlist, evsel) {
> > +			struct hists *hists = evsel__hists(evsel);
> > +
> > +			if (perf_evsel__is_dummy_tracking(evsel))
> > +				continue;
> > +
> > +			hists__mt_resort(hists, &mt->hists[evsel->idx]);
> > +
> > +			/* Non-group events are considered as leader */
> > +			if (symbol_conf.event_group &&
> > +			    !perf_evsel__is_group_leader(evsel)) {
> > +				struct hists *leader_hists;
> > +
> > +				leader_hists = evsel__hists(evsel->leader);
> > +				hists__match(leader_hists, hists);
> > +				hists__link(leader_hists, hists);
> 
> hum, could you please describe/comment on why is this needed?

This is because it skips report__collapse_hists() when multi-thread
processing is enabled.  For multi-thread, it needs to collect
per-thread hists into a global hists.  This step is very similar to
hists__collapse_resort() and called regardless of sort keys, so it
skips to call the report__collapse_hists().

But I think it should be called after collapsing all per-thread hists.
I'll move it out of the loop.

Thanks,
Namhyung
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