linux-kernel - Re: [PATCH 1/2] perf record: Fix "--per-thread" option for hybrid machines

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Date:   Wed, 6 Jul 2022 20:00:41 +0800
From:   Xing Zhengjun <zhengjun.xing@...ux.intel.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>, acme@...nel.org,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...el.com, jolsa@...nel.org, namhyung@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        irogers@...gle.com, ak@...ux.intel.com,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 1/2] perf record: Fix "--per-thread" option for hybrid
 machines



On 7/4/2022 9:22 PM, Liang, Kan wrote:
> 
> 
> On 7/1/2022 10:35 PM, zhengjun.xing@...ux.intel.com wrote:
>> From: Zhengjun Xing <zhengjun.xing@...ux.intel.com>
>>
>> Commit b91e5492f9d7 ("perf record: Add a dummy event on hybrid systems to
>> collect metadata records") adds a dummy event on hybrid systems to fix 
>> the
>> symbol "unknown" issue when the workload is created in a P-core but runs
>> on an E-core. When "--per-thread" is enabled, the nr_cpus is reduced 
>> to 1,
>>   adding a dummy event is useless for this issue, and it will also cause
> 
> A dummy event is required since a mmap event may be loaded at runtime on 
> any CPU. Thanks Adrian to point it out.
> 

There will be a kernel patch to fix the "mmap fail" issue, I will drop 
this one and continue to fix other "per-thread" issues based on the 
kernel patch.


> Thanks,
> Kan
> 
>> "failed to mmap with 22 (Invalid argument)". This patch stops adding 
>> dummy
>> events when the option "--per-thread" is enabled, then the option can 
>> work
>> on hybrid machines.
>>
>> Before:
>>
>>   # ./perf record -e cycles:u --per-thread  sleep 1
>>   failed to mmap with 22 (Invalid argument)
>>
>> After:
>>
>>   # ./perf record -e cycles:u --per-thread  sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.002 MB perf.data (6 samples) ]
>>
>> Fixes: b91e5492f9d7 ("perf record: Add a dummy event on hybrid systems 
>> to collect metadata records")
>> Signed-off-by: Zhengjun Xing <zhengjun.xing@...ux.intel.com>
>> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
>> ---
>>   tools/perf/builtin-record.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index e1edd4e98358..44ea2dd424fe 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -1223,7 +1223,7 @@ static int record__open(struct record *rec)
>>        * of waiting or event synthesis.
>>        */
>>       if (opts->initial_delay || target__has_cpu(&opts->target) ||
>> -        perf_pmu__has_hybrid()) {
>> +        (perf_pmu__has_hybrid() && !opts->target.per_thread)) {
>>           pos = evlist__get_tracking_event(evlist);
>>           if (!evsel__is_dummy_event(pos)) {
>>               /* Set up dummy event. */

-- 
Zhengjun Xing