From: "Jin, Yao" <yao.jin@linux.intel.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: acme@kernel.org, jolsa@kernel.org, peterz@infradead.org,
mingo@redhat.com, alexander.shishkin@linux.intel.com,
Linux-kernel@vger.kernel.org, ak@linux.intel.com,
kan.liang@intel.com, yao.jin@intel.com, irogers@google.com,
Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH v2] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event
Date: Thu, 23 Jul 2020 09:01:46 +0800 [thread overview]
Message-ID: <6f732f7f-7c5a-726f-5b09-2c6761f3b534@linux.intel.com> (raw)
In-Reply-To: <20200722110810.GD981884@krava>
Hi Jiri, Adrian,
On 7/22/2020 7:08 PM, Jiri Olsa wrote:
> On Wed, Jul 22, 2020 at 01:00:03PM +0800, Jin, Yao wrote:
>
> SNIP
>
>>>>
>>>> If we use -IXMM0, the attr>sample_regs_intr will be set with
>>>> PERF_REG_EXTENDED_MASK bit.
>>>>
>>>> It doesn't make sense to set attr->sample_regs_intr for a
>>>> software dummy event.
>>>>
>>>> This patch adds dummy event checking before setting
>>>> attr->sample_regs_intr and attr->sample_regs_user.
>>>>
>>>> After:
>>>> # ./perf record -e cycles:p -IXMM0 -a -- sleep 1
>>>> [ perf record: Woken up 1 times to write data ]
>>>> [ perf record: Captured and wrote 0.413 MB perf.data (45 samples) ]
>>>>
>>>> v2:
>>>> ---
>>>> Rebase to perf/core
>>>>
>>>> Fixes: 0a892c1c9472 ("perf record: Add dummy event during system wide synthesis")
>>>> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
>>>> ---
>>>> tools/perf/util/evsel.c | 6 ++++--
>>>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>>>> index 9aa51a65593d..11794d3b7879 100644
>>>> --- a/tools/perf/util/evsel.c
>>>> +++ b/tools/perf/util/evsel.c
>>>> @@ -1014,12 +1014,14 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
>>>> if (callchain && callchain->enabled && !evsel->no_aux_samples)
>>>> evsel__config_callchain(evsel, opts, callchain);
>>>> - if (opts->sample_intr_regs && !evsel->no_aux_samples) {
>>>> + if (opts->sample_intr_regs && !evsel->no_aux_samples &&
>>>> + !evsel__is_dummy_event(evsel)) {
>>>
>>> hum, I thought it'd look something like this:
>>>
>>> if (opts->sample_intr_regs && (!evsel->no_aux_samples || !evsel__is_dummy_event(evsel))
>>>
>>> but I'm not sure how no_aux_samples flag works exactly.. so it might be
>>> correct.. just making sure ;-)
>>>
>>> cc-ing Adrian
>>>
>>> jirka
>>>
>>>
>>
>> no_aux_samples is set to false by default and it's only set to true by pt, right?
>>
>> So most of the time, !evsel->no_aux_samples is always true.
>>
>> if (opts->sample_intr_regs && (!evsel->no_aux_samples || !evsel__is_dummy_event(evsel)) {
>> attr->sample_regs_intr = opts->sample_intr_regs;
>> evsel__set_sample_bit(evsel, REGS_INTR);
>> }
>>
>> So even if the evsel is dummy event, the condition check is true. :(
>>
>> Or maybe I misunderstand anything?
>
> I was just curious, because I did not follow the no_aux_samples
> usage in detail.. so how about a case where:
>
> evsel->no_aux_samples == true and evsel__is_dummy_event(evsel) = false
>
> then the original condition will be false for non dummy event
>
> (opts->sample_intr_regs && !evsel->no_aux_samples && !evsel__is_dummy_event(evsel))
>
> is that ok?
>
I searched the perf source and found the no_aux_samples was only set to true in intel-pt.c. So I
assume for the non-pt usage, the no_aux_samples is always false.
For non-pt usage,
(opts->sample_intr_regs && !evsel->no_aux_samples && !evsel__is_dummy_event(evsel)) is equal to
(opts->sample_intr_regs && !evsel__is_dummy_event(evsel))
For pt usage, we need to consider the case that evsel__is_dummy_event(evsel) is true or false.
If evsel__is_dummy_event(evsel) is true:
(opts->sample_intr_regs && !evsel->no_aux_samples && !evsel__is_dummy_event(evsel)) is false.
It's expected.
If evsel__is_dummy_event(evsel) is false:
(opts->sample_intr_regs && !evsel->no_aux_samples && !evsel__is_dummy_event(evsel)) is equal to
(opts->sample_intr_regs && !evsel->no_aux_samples)
That's the current code logic.
So I think the condition "(opts->sample_intr_regs && !evsel->no_aux_samples &&
!evsel__is_dummy_event(evsel))" looks reasonable.
Adrian, please correct me if I'm wrong here.
Thanks
Jin Yao
> jirka
>
next prev parent reply other threads:[~2020-07-23 1:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-20 1:00 [PATCH v2] perf evsel: Don't set sample_regs_intr/sample_regs_user for dummy event Jin Yao
2020-07-20 9:17 ` Jiri Olsa
2020-07-22 5:00 ` Jin, Yao
2020-07-22 11:08 ` Jiri Olsa
2020-07-23 1:01 ` Jin, Yao [this message]
2020-07-29 7:23 ` Jin, Yao
2020-08-04 7:06 ` Adrian Hunter
2020-08-04 12:06 ` Arnaldo Carvalho de Melo
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