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Date:   Tue, 30 Jan 2018 16:04:54 +0100
From:   Jiri Olsa <jolsa@redhat.com>
To:     "Liang, Kan" <kan.liang@linux.intel.com>
Cc:     Stephane Eranian <eranian@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH V3 0/5] bugs fix for large PEBS mmap read and rdpmc read
Message-ID: <20180130150454.GE29098@krava>
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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@linux.intel.com> wrote:
> > > > 
> > > > From: Kan Liang <kan.liang@linux.intel.com>
> > > > 
> > > > ------
> > > > 
> > > > 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

jirka