Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
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>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <44645529-0ee6-fe69-bc03-fefbc6f73d4d@huawei.com>
Date:   Tue, 18 Jul 2023 17:30:48 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.1
MIME-Version: 1.0
In-Reply-To: <5797e5a7-a85f-4f7c-1649-88f8f9ff7a6b@intel.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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?

Thanks,
Yang