linux-kernel - Re: [PATCH] perf report: Provide libtraceevent with a kernel symbol resolver

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Date:   Mon, 22 Jan 2018 01:25:03 +0800
From:   Wang YanQing <udknight@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     acme@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf report: Provide libtraceevent with a kernel symbol
 resolver

On Fri, Jan 19, 2018 at 07:57:59PM +0100, Jiri Olsa wrote:
> On Thu, Jan 18, 2018 at 10:22:30PM +0800, Wang YanQing wrote:
> > On Thu, Jan 18, 2018 at 10:43:18AM +0100, Jiri Olsa wrote:
> > > On Wed, Jan 17, 2018 at 12:48:12AM +0800, Wang YanQing wrote:
> > > > On Mon, Jan 15, 2018 at 11:06:11AM +0100, Jiri Olsa wrote:
> > > > > On Mon, Jan 15, 2018 at 12:47:32PM +0800, Wang YanQing wrote:
> > > > > > So that beautifiers wanting to resolve kernel function addresses to
> > > > > > names can do its work, and when we use "perf report" for output of
> > > > > > "perf kmem record", we will get kernel symbol output.
> > > > > > 
> > > > > > Signed-off-by: Wang YanQing <udknight@...il.com>
> > > > > > ---
> > > > > >  tools/perf/builtin-report.c | 9 +++++++++
> > > > > >  1 file changed, 9 insertions(+)
> > > > > > 
> > > > > > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > > > > > index dd4df9a..7b65100 100644
> > > > > > --- a/tools/perf/builtin-report.c
> > > > > > +++ b/tools/perf/builtin-report.c
> > > > > > @@ -1317,6 +1317,15 @@ int cmd_report(int argc, const char **argv)
> > > > > >  		report.range_num = 1;
> > > > > >  	}
> > > > > >  
> > > > > > +	if (session->tevent.pevent &&
> > > > > > +	    pevent_set_function_resolver(session->tevent.pevent,
> > > > > > +					 machine__resolve_kernel_addr,
> > > > > > +					 &session->machines.host) < 0) {
> > > > > > +		pr_err("%s: failed to set libtraceevent function resolver\n",
> > > > > > +		       __func__);
> > > > > > +		return -1;
> > > > > > +	}
> > > > > 
> > > > > why not calling the wrapper trace_event__register_resolver?
> > > > The reason is the same as builtin-script doesn't use trace_event__register_resolver,
> > > > because we only use report and script to analyze offline perf.data, and there could
> > > > be no tracepoints in perf.data.
> > > 
> > > hum, I missed this functionality.. so we need this even if there
> > > are no tracepoints in the perf.data?
> > 
> > In "perf report", when there are tracepoints in perf.data, session->tevent.pevent
> > will be initialized in trace-event-read.c:trace_report, then "if (session->tevent.pevent"
> > will become true, and we should calling pevent_set_function_resolver.
> > 
> > But if we calling trace_event__register_resolver, then it will initialize tevent.pevent
> > no matter whether there are tracepoints in perf.data.
> 
> ok, should we call it from perf_session__read_header then?
> below perf_evlist__prepare_tracepoint_events perhaps

No, I think we can't do it in perf_session__read_header,
because perf_session__new calls perf_session__create_kernel_maps
to initialize machines.host after calling perf_session__open, and
pevent_set_function_resolver needs it. 

Although it is possible to place pevent_set_function_resolver at
the tail of perf_session__new, but I don't think it is a better
choice for us, because tools like "perf kmem stat" doesn't need it,
"perf kmem stat" has itself way to prepare and display the symbols
of callsites.

I think the current calling place of pevent_set_function_resolver
for "perf report" is the right place.

Thanks.
> jirka