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Subject: Re: [PATCH v2 5/7] perf evlist: Skip dummy event sample_type check
 for evlist_config
To:     Adrian Hunter <adrian.hunter@intel.com>, <peterz@infradead.org>,
        <mingo@redhat.com>, <acme@kernel.org>, <mark.rutland@arm.com>,
        <alexander.shishkin@linux.intel.com>, <jolsa@kernel.org>,
        <namhyung@kernel.org>, <irogers@google.com>,
        <kan.liang@linux.intel.com>, <james.clark@arm.com>,
        <tmricht@linux.ibm.com>, <ak@linux.intel.com>,
        <anshuman.khandual@arm.com>, <linux-kernel@vger.kernel.org>,
        <linux-perf-users@vger.kernel.org>
References: <20230715032915.97146-1-yangjihong1@huawei.com>
 <20230715032915.97146-6-yangjihong1@huawei.com>
 <5797e5a7-a85f-4f7c-1649-88f8f9ff7a6b@intel.com>
 <44645529-0ee6-fe69-bc03-fefbc6f73d4d@huawei.com>
 <c4b7fb70-7b2e-74e9-576f-33b29e8801cd@intel.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <77ea9309-da6f-f7b9-a822-b371e0f832d3@huawei.com>
Date:   Tue, 18 Jul 2023 18:17:17 +0800
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Hello,

On 2023/7/18 17:56, Adrian Hunter wrote:
> On 18/07/23 12:30, Yang Jihong wrote:
>> Hello,
>>
>> On 2023/7/17 22:41, Adrian Hunter wrote:
>>> On 15/07/23 06:29, Yang Jihong wrote:
>>>> The dummp event does not contain sampls data. Therefore, sample_type does
>>>> not need to be checked.
>>>>
>>>> Currently, the sample id format of the actual sampling event may be changed
>>>> after the dummy event is added.
>>>>
>>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>>>> ---
>>>>    tools/perf/util/record.c | 7 +++++++
>>>>    1 file changed, 7 insertions(+)
>>>>
>>>> diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
>>>> index 9eb5c6a08999..0240be3b340f 100644
>>>> --- a/tools/perf/util/record.c
>>>> +++ b/tools/perf/util/record.c
>>>> @@ -128,6 +128,13 @@ void evlist__config(struct evlist *evlist, struct record_opts *opts, struct call
>>>>            evlist__for_each_entry(evlist, evsel) {
>>>>                if (evsel->core.attr.sample_type == first->core.attr.sample_type)
>>>>                    continue;
>>>> +
>>>> +            /*
>>>> +             * Skip the sample_type check for the dummy event
>>>> +             * because it does not have any samples anyway.
>>>> +             */
>>>> +            if (evsel__is_dummy_event(evsel))
>>>> +                continue;
>>>
>>> Sideband event records have "ID samples" so the sample type still matters.
>>>
>> Okay, will remove this patch in next version.
>>
>> Can I ask a little more about this?
>>
>> Use PERF_SAMPLE_IDENTIFICATION instead of PERF_SAMPLE_ID because for samples of type PERF_RECORD_SAMPLE, there may be different record formats due to different *sample_type* settings, so the fixed SAMPLE_ID  location mode PERF_SAMPLE_NAME is required here.
>>
>> However, for the sideband event, the samples of the PERF_RECORD_SAMPLE type is not recorded (only PERF_RECORD_MMAP, PERF_RECORD_COMM, and so on). Therefore, the "use sample identifier "check can be skipped here.
>>
>> That's my understanding of PERF_SAMPLE_IDENTIFICATION . If there is any error, please help to correct it.
>>
>> *Sideband event records have "ID samples" so the sample type still matters.*
>>
>> Does this mean that sideband will also record samples of type PERF_RECORD_SAMPLE? What exactly is the sampling data?
> 
> No.  There are additional members as defined by struct sample_id for PERF_RECORD_MMAP:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/perf_event.h?h=v6.4#n872
> 
I'm sorry, maybe my comments didn't make it clear.
I mean, can we skip the "use_sample_identifier" check here?

That is, set sample_type to *XXX|PERF_SAMPLE_ID* instead of 
*XXX|PERF_SAMPLE_IDENTIFICATION*

Thanks,
Yang