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Message-ID: <35090c62-466a-aec8-b1a3-69def959c1c6@linux.intel.com>
Date: Tue, 30 Jan 2018 10:25:27 -0500
From: "Liang, Kan" <kan.liang@...ux.intel.com>
To: Jiri Olsa <jolsa@...hat.com>
Cc: Stephane Eranian <eranian@...gle.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 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.
Thanks,
Kan
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