Re: [PATCH V3 0/5] bugs fix for large PEBS mmap read and rdpmc read

[Liang, Kan]

On 1/30/2018 10:04 AM, Jiri Olsa wrote:
> On Tue, Jan 30, 2018 at 09:59:15AM -0500, Liang, Kan wrote:
> > On 1/30/2018 8:39 AM, Jiri Olsa wrote:
> > > On Tue, Jan 30, 2018 at 01:16:39AM -0800, Stephane Eranian wrote:
> > > > Hi,
> > > >
> > > > On Mon, Jan 29, 2018 at 8:29 AM, <kan.liang@xxxxxxxxxxxxxxx> wrote:
> > > > > From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> > > > >
> > > > > ------
> > > > >
> > > > > Changes since V2:
> > > > >    - Refined the changelog
> > > > >    - Introduced specific read function for large PEBS.
> > > > >      The previous generic PEBS read function is confusing.
> > > > >      Disabled PMU in pmu::read() path for large PEBS.
> > > > >      Handled the corner case when reload_times == 0.
> > > > >    - Modified the parameter of intel_pmu_save_and_restart_reload()
> > > > >      Discarded local64_cmpxchg
> > > > >    - Added fixes tag
> > > > >    - Added WARN to handle reload_times == 0 || reload_val == 0
> > > > >
> > > > > Changes since V1:
> > > > >    - Check PERF_X86_EVENT_AUTO_RELOAD before call
> > > > >      intel_pmu_save_and_restore()
> > > >
> > > > It is not yet clear to me why PERF_SAMPLE_PERIOD is not allowed
> > > > with large PEBS. Large PEBS requires fixed period. So the kernel could
> > > > make up the period from the event and store it in the sampling buffer.
> > > >
> > > > I tried using large PEBS recently, and despite trying different option
> > > > combination of perf record, I was not able to get it to work.
> > > >
> > > > $ perf record  -c 1  -e cpu/event=0xd1,umask=0x10,period=19936/pp
> > > > --no-timestamp --no-period -a -C 0
> > > >
> > > > But I was able to make this work with a much older kernel.
> > > >
> > > > Another annoyance I ran into is with perf record requiring -c period
> > > > in order not to set
> > > > PERF_SAMPLE_PERIOD in the event.
> > > >
> > > > If I do:
> > > > perf record  -c 1  -e cpu/event=0xd1,umask=0x10,period=19936/pp
> > > > --no-timestamp --no-period -a -C 0
> > > >
> > > > I get
> > > >
> > > > perf_event_attr:
> > > >     type                             4
> > > >     size                             112
> > > >     config                           0x10d1
> > > >     { sample_period, sample_freq }   199936
> > > >     sample_type                      IP|TID|CPU
> > > >
> > > > But if I do:
> > > > perf record  -e cpu/event=0xd1,umask=0x10,period=19936/pp
> > > > --no-timestamp --no-period -a -C 0
> > > >
> > > > I get
> > > >
> > > > perf_event_attr:
> > > >     type                             4
> > > >     size                             112
> > > >     config                           0x10d1
> > > >     { sample_period, sample_freq }   199936
> > > >     sample_type                      IP|TID|CPU|PERIOD
> > > >
> > > > Perf should check if all events have a period=, then it should not
> > > > pass PERF_SAMPLE_PERIOD, even
> > > > more so when only one event is defined.
> > > >
> > > > Also it does not seem to honor --no-period.
> > >
> > > yep, there's a bug in period=x term handling
> > > we did not re/set the sample_type based on that
> > >
> > > attached patch fixes that for me, also takes into account
> > > the --no/-period options
> > >
> > > jirka
> > >
> > >
> > > ---
> > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > > index f251e824edac..907267206973 100644
> > > --- a/tools/perf/builtin-record.c
> > > +++ b/tools/perf/builtin-record.c
> > > @@ -1566,7 +1566,8 @@ static struct option __record_options[] = {
> > >    	OPT_BOOLEAN_SET('T', "timestamp", &record.opts.sample_time,
> > >    			&record.opts.sample_time_set,
> > >    			"Record the sample timestamps"),
> > > -	OPT_BOOLEAN('P', "period", &record.opts.period, "Record the sample period"),
> > > +	OPT_BOOLEAN_SET('P', "period", &record.opts.period, &record.opts.period_set,
> > > +			"Record the sample period"),
> > >    	OPT_BOOLEAN('n', "no-samples", &record.opts.no_samples,
> > >    		    "don't sample"),
> > >    	OPT_BOOLEAN_SET('N', "no-buildid-cache", &record.no_buildid_cache,
> > > diff --git a/tools/perf/perf.h b/tools/perf/perf.h
> > > index 2357f4ccc9c7..cfe46236a5e5 100644
> > > --- a/tools/perf/perf.h
> > > +++ b/tools/perf/perf.h
> > > @@ -50,6 +50,7 @@ struct record_opts {
> > >    	bool	     sample_time_set;
> > >    	bool	     sample_cpu;
> > >    	bool	     period;
> > > +	bool	     period_set;
> > >    	bool	     running_time;
> > >    	bool	     full_auxtrace;
> > >    	bool	     auxtrace_snapshot_mode;
> > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > > index 66fa45198a11..ff359c9ece2e 100644
> > > --- a/tools/perf/util/evsel.c
> > > +++ b/tools/perf/util/evsel.c
> > > @@ -745,12 +745,14 @@ static void apply_config_terms(struct perf_evsel *evsel,
> > >    			if (!(term->weak && opts->user_interval != ULLONG_MAX)) {
> > >    				attr->sample_period = term->val.period;
> > >    				attr->freq = 0;
> > > +				perf_evsel__reset_sample_bit(evsel, PERIOD);
> > >    			}
> > >    			break;
> > >    		case PERF_EVSEL__CONFIG_TERM_FREQ:
> > >    			if (!(term->weak && opts->user_freq != UINT_MAX)) {
> > >    				attr->sample_freq = term->val.freq;
> > >    				attr->freq = 1;
> > > +				perf_evsel__set_sample_bit(evsel, PERIOD);
> > >    			}
> >
> > If we do so, some events could be in fixed mode without PERIOD set. Other
> > events could be in freq mode with PERIOD set.
>
> it also sets the attr->freq, so it's not in fixed mode

I mean the TERM_PERIOD. It probably enable the large PEBS.
>>>    				attr->freq = 0;
>>> +				perf_evsel__reset_sample_bit(evsel, PERIOD);

The events in fixed mode could enable large PEBS. Events in freq mode 
should not enable large PEBS.
I think that could be a problem if some events try to enable large PEBS, 
while others not.

Thanks,
Kan