linux-kernel - Re: [PATCH 2/5] perf unwind: Do not look at globals

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Message-ID: <20180116200520.GG16107@kernel.org>
Date:   Tue, 16 Jan 2018 17:05:20 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        David Ahern <dsahern@...il.com>,
        Hendrick Brueckner <brueckner@...ux.vnet.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Richter <tmricht@...ux.vnet.ibm.com>,
        Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 2/5] perf unwind: Do not look at globals

Em Tue, Jan 16, 2018 at 08:49:09PM +0100, Jiri Olsa escreveu:
> On Tue, Jan 16, 2018 at 03:26:50PM -0300, Arnaldo Carvalho de Melo wrote:
> 
> SNIP
> 
> > diff --git a/tools/perf/builtin-c2c.c b/tools/perf/builtin-c2c.c
> > index c0debc3f79b6..c0815a37fdb5 100644
> > --- a/tools/perf/builtin-c2c.c
> > +++ b/tools/perf/builtin-c2c.c
> > @@ -2390,9 +2390,10 @@ static int setup_callchain(struct perf_evlist *evlist)
> >  	enum perf_call_graph_mode mode = CALLCHAIN_NONE;
> >  
> >  	if ((sample_type & PERF_SAMPLE_REGS_USER) &&
> > -	    (sample_type & PERF_SAMPLE_STACK_USER))
> > +	    (sample_type & PERF_SAMPLE_STACK_USER)) {
> >  		mode = CALLCHAIN_DWARF;
> > -	else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> > +		dwarf_callchain_users = true;
> > +	} else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> >  		mode = CALLCHAIN_LBR;
> >  	else if (sample_type & PERF_SAMPLE_CALLCHAIN)
> >  		mode = CALLCHAIN_FP;
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index dd4df9a5cd06..6593779224d5 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -338,9 +338,10 @@ static int report__setup_sample_type(struct report *rep)
> >  
> >  	if (symbol_conf.use_callchain || symbol_conf.cumulate_callchain) {
> >  		if ((sample_type & PERF_SAMPLE_REGS_USER) &&
> > -		    (sample_type & PERF_SAMPLE_STACK_USER))
> > +		    (sample_type & PERF_SAMPLE_STACK_USER)) {
> >  			callchain_param.record_mode = CALLCHAIN_DWARF;
> > -		else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> > +			dwarf_callchain_users = true;
> > +		} else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> >  			callchain_param.record_mode = CALLCHAIN_LBR;
> >  		else
> >  			callchain_param.record_mode = CALLCHAIN_FP;
> > diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> > index c1cce474c0f1..08bc818f371b 100644
> > --- a/tools/perf/builtin-script.c
> > +++ b/tools/perf/builtin-script.c
> > @@ -2919,9 +2919,10 @@ static void script__setup_sample_type(struct perf_script *script)
> >  
> >  	if (symbol_conf.use_callchain || symbol_conf.cumulate_callchain) {
> >  		if ((sample_type & PERF_SAMPLE_REGS_USER) &&
> > -		    (sample_type & PERF_SAMPLE_STACK_USER))
> > +		    (sample_type & PERF_SAMPLE_STACK_USER)) {
> >  			callchain_param.record_mode = CALLCHAIN_DWARF;
> > -		else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> > +			dwarf_callchain_users = true;
> > +		} else if (sample_type & PERF_SAMPLE_BRANCH_STACK)
> >  			callchain_param.record_mode = CALLCHAIN_LBR;
> >  		else
> >  			callchain_param.record_mode = CALLCHAIN_FP;
> > diff --git a/tools/perf/tests/dwarf-unwind.c b/tools/perf/tests/dwarf-unwind.c
> > index ac40e05bcab4..260418969120 100644
> > --- a/tools/perf/tests/dwarf-unwind.c
> > +++ b/tools/perf/tests/dwarf-unwind.c
> > @@ -173,6 +173,7 @@ int test__dwarf_unwind(struct test *test __maybe_unused, int subtest __maybe_unu
> >  	}
> >  
> >  	callchain_param.record_mode = CALLCHAIN_DWARF;
> > +	dwarf_callchain_users = true;
> >  
> >  	if (init_live_machine(machine)) {
> >  		pr_err("Could not init machine\n");
> > diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> > index 082505d08d72..32ef7bdca1cf 100644
> > --- a/tools/perf/util/callchain.c
> > +++ b/tools/perf/util/callchain.c
> > @@ -37,6 +37,15 @@ struct callchain_param callchain_param = {
> >  	CALLCHAIN_PARAM_DEFAULT
> >  };
> >  
> > +/*
> > + * Are there any events usind DWARF callchains?
> > + *
> > + * I.e.
> > + *
> > + * -e cycles/call-graph=dwarf/
> > + */
> > +bool dwarf_callchain_users;
> 
> hum, I don't follow.. this bool seems to mirror the usage of
> 'param->record_mode = CALLCHAIN_DWARF', whats the difference?
> 
> also, the patch title says 'Do not look at globals', while inside you

The first version didn't look at globals, the second one doesn't look at
an _specific_ global variable, the global config for --call-graph, which
is a global variable, callchain_param, which _we_ can't touch at
apply_config_terms(), since that is about _just_ that event, not all of
them.

> add new global dwarf_callchain_users and work with it.. what do I miss?
> 
> I'll check tomorrow with clean head ;-)

Look closely at apply_config_terms() it passes a _local_ variable to

                        perf_evsel__config_callchain(evsel, opts, &param);

It will not affect any globals that tools/perf/util/unwind-libunwind-local.c
could possibly use... and that is the problem. :-)

The right fix, as I said, is more involved and may allow us to remove
these two global variables, both callchain_param and
dwarf_callchain_users.

We need to have per-evsel unwind ops, per thread addr_space continues to
be used by the dwarf unwinder _for the events sampled in that thread_,
etc.

The prepare_unwind is to be made to evsel and thread (for thread we need
to look at one of its executable maps, to determine if it is 32-bit or
64-bit, etc, but not necessarily at that insert_map part, etc).

- Arnaldo