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Date: Tue, 30 Jan 2018 11:48:18 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Stephane Eranian <eranian@...gle.com>
Cc: Jiri Olsa <jolsa@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH V3 0/5] bugs fix for large PEBS mmap read and rdpmc read
On 1/30/2018 11:36 AM, Stephane Eranian wrote:
> On Tue, Jan 30, 2018 at 7:25 AM, Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>
>>
>> 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@...ux.intel.com> wrote:
>>>>>>>
>>>>>>>
>>>>>>> From: Kan Liang <kan.liang@...ux.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
>>>
>>
>> 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.
>>
> You only enable large PEBS if 100% of the events use fixed periods,
> either via -c period
> or because they all use individual period=p. The --no-period could
> also be used to remove
> the period for measurements where the period is not needed.
Oh, right, the kernel has already guaranteed that.
if (cpuc->n_pebs == cpuc->n_large_pebs) {
threshold = ds->pebs_absolute_maximum -
x86_pmu.max_pebs_events * x86_pmu.pebs_record_size;
} else {
Sorry for the noise.
jirka's patch looks good to me.
Thanks,
Kan
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