linux-kernel - Re: [PATCH] perf record: Add snapshot mode support for perf's regular events

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Date:	Tue, 24 Nov 2015 08:24:07 -0700
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:	Yunlong Song <yunlong.song@...wei.com>, a.p.zijlstra@...llo.nl,
	paulus@...ba.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
	wangnan0@...wei.com, namhyung@...nel.org, ast@...nel.org,
	masami.hiramatsu.pt@...achi.com, kan.liang@...el.com,
	adrian.hunter@...el.com, jolsa@...nel.org, bp@...en8.de,
	jean.pihet@...aro.org, rric@...nel.org, xiakaixu@...wei.com,
	hekuang@...wei.com
Subject: Re: [PATCH] perf record: Add snapshot mode support for perf's regular
 events

On 11/24/15 8:20 AM, Arnaldo Carvalho de Melo wrote:
> Em Tue, Nov 24, 2015 at 08:06:41AM -0700, David Ahern escreveu:
>> On 11/24/15 7:00 AM, Yunlong Song wrote:
>>> +static int record__write(struct record *rec, void *bf, size_t size)
>>> +{
>>> +	if (rec->memory.size && memory_enabled) {
>>> +		if (perf_memory__write(&rec->memory, bf, size) < 0) {
>>> +			pr_err("failed to write memory data, error: %m\n");
>>> +			return -1;
>>> +		}
>>> +	} else {
>>> +		if (perf_data_file__write(rec->session->file, bf, size) < 0) {
>>> +			pr_err("failed to write perf data, error: %m\n");
>>> +			return -1;
>>> +		}
>>> +		rec->bytes_written += size;
>>>   	}
>>>
>>> -	rec->bytes_written += size;
>>>   	return 0;
>>>   }
>>>
>>> @@ -86,6 +214,8 @@ static int record__mmap_read(struct record *rec, int idx)
>>>   	if (old == head)
>>>   		return 0;
>>>
>>> +	memory_enabled = 1;
>>> +
>>>   	rec->samples++;
>>>
>>>   	size = head - old;
>>> @@ -113,6 +243,7 @@ static int record__mmap_read(struct record *rec, int idx)
>>>   	md->prev = old;
>>>   	perf_evlist__mmap_consume(rec->evlist, idx);
>>>   out:
>>> +	memory_enabled = 0;
>>>   	return rc;
>>>   }
>>>
>>
>> So you are basically ignoring all samples until SIGUSR2 is received. That
>
> No, he is not, its just that his code is difficult to follow, has to be
> rewritten, but he is ignoring just PERF_RECORD_SAMPLE events, so it
> will..
>
>> means the resulting data file will have limited history of task events for
>
> ... have a complete history of task events, since PERF_RECORD_FORK, etc
> are not being ignored.
>
> No?

perf-record does not process events, it only writes to a file. If that 
is skipped then it skips all events regardless of type.

David

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