linux-kernel - Re: [PATCH v2 08/15] perf record: write trace data into mmap trace files

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Message-ID: <adc90ef5-58cc-8578-13f7-cbce895f1a28@gmail.com>
Date:   Mon, 26 Oct 2020 11:52:21 +0300
From:   Alexei Budankov <budankov.lore@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        budankov.lore@...il.com
Subject: Re: [PATCH v2 08/15] perf record: write trace data into mmap trace
 files


On 24.10.2020 18:44, Jiri Olsa wrote:
> On Wed, Oct 21, 2020 at 07:02:56PM +0300, Alexey Budankov wrote:
> 
> SNIP
> 
>>  
>>  	record__synthesize(rec, true);
>> -	/* this will be recalculated during process_buildids() */
>> -	rec->samples = 0;
>>  
>>  	if (!err) {
>>  		if (!rec->timestamp_filename) {
>> @@ -2680,9 +2709,12 @@ int cmd_record(int argc, const char **argv)
>>  
>>  	}
>>  
>> -	if (rec->opts.kcore)
>> +	if (rec->opts.kcore || record__threads_enabled(rec))
>>  		rec->data.is_dir = true;
>>  
>> +	if (record__threads_enabled(rec))
>> +		rec->opts.affinity = PERF_AFFINITY_CPU;
> 
> so all the threads will pin to cpu and back before reading?

No, they will not back. Thread mask compares to mmap mask before
read and the thread migrates if masks don't match. This happens
once on the first mmap read. So explicit pinning can be avoided.

Alexei