linux-kernel - Re: [PATCH v3 6/8] perf session: Move event read code to separate function

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Message-ID: <d630cf0d-1bb5-0527-411a-c70a01e2ddea@linux.intel.com>
Date:   Mon, 11 Oct 2021 19:40:33 +0300
From:   "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexander Antonov <alexander.antonov@...ux.intel.com>,
        Alexei Budankov <abudankov@...wei.com>,
        Riccardo Mancini <rickyman7@...il.com>
Subject: Re: [PATCH v3 6/8] perf session: Move event read code to separate
 function



On 11.10.2021 16:21, Jiri Olsa wrote:
> On Mon, Oct 11, 2021 at 12:53:30PM +0300, Bayduraev, Alexey V wrote:
>>
>>
>> On 11.10.2021 12:08, Bayduraev, Alexey V wrote:
>>>
>>> On 08.10.2021 17:38, Jiri Olsa wrote:
>>>> On Fri, Oct 08, 2021 at 11:42:18AM +0300, Bayduraev, Alexey V wrote:
>>>>>
>>>>>
>>>>> On 08.10.2021 10:33, Jiri Olsa wrote:
>>>>>> On Thu, Oct 07, 2021 at 01:25:41PM +0300, Alexey Bayduraev wrote:
>>>>>>
>>>>>> SNIP
>>>>>>
>>>>>>>  static int
>>>>>>> -reader__process_events(struct reader *rd, struct perf_session *session,
>>>>>>> -		       struct ui_progress *prog)
>>>>>>> +reader__read_event(struct reader *rd, struct perf_session *session,
>>>>>>> +		   struct ui_progress *prog)
>>>
>>> SNIP
>>>
>>>>>>
>>>>>> active_decomp should be set/unset within reader__process_events,
>>>>>> not just for single event read, right?
>>>>>
>>>>> No, it should be set before perf_session__process_event/process_decomp_events
>>>>> and unset after these calls. So active_decomp setting/unsetting is moved in
>>>>> this patch to the reader__read_event function. This is necessary for multiple
>>>>> trace reader because it could call reader__read_event in round-robin manner.
>>>>
>>>> hum, is that code already in? I can't see this happening in current code
>>>
>>> Probably I don't understand the question. In [PATCH v3 2/8] I introduced 
>>> active_decomp pointer in perf_session. It is initialized by a pointer to the 
>>> decompressor object in perf_session. In reader__process_events it is set to 
>>> the reader decompressor object. And it is reset to the session decompressor 
>>> object at exit. In this case we do not need to reset it after each 
>>> perf_session__process_event because this code reads events in loop with 
>>> constant reader object. Maybe setting of active_decomp should be at the 
>>> entrance to the reader__process_events, not before reader__process_events, 
>>> in [PATCH v3 2/8]. All this code is new.
>>
>> We set active_decomp for perf_session__process_event (rd->process() in our
>> case) and for __perf_session__process_decomp_events, active_decomp is not 
>> necessary for other parts of reader__process_events.
> 
> so what I see in the code is:
> 
> __perf_session__process_events
> {
> 	struct reader rd;
> 
> 	reader__process_events(rd)
> 	{
> 		reader__read_event(rd)
> 		{
> ->			session->active_decomp = &rd->decomp_data;
> 			rd->process(...
> ->			session->active_decomp = &session->decomp_data;
> 		}
> 
> 	}
> }
> 
> 
> we set session->active_decomp for each event that we process
> and I don't understand why we can't do that just once in
> __perf_session__process_events, so it'd be like:
> 
> __perf_session__process_events
> {
> 	struct reader rd;
> 
> ->	session->active_decomp = &rd->decomp_data;
> 
> 	reader__process_events(rd)
> 	{
> 		reader__read_event(rd)
> 		{
> 			rd->process(...
> 		}
> 
> 	}
> 
> ->	session->active_decomp = &session->decomp_data;
> }
> 
> 
> or within reader__process_events if it's more convenient

Now I got it, thanks ;)

With your suggestion, for multiple trace reader, we should always 
remember to switch active_decomp when switching the reader object, 
just passing the current reader pointer to the reader__read_event 
function will not be enough. I thought it would be better to hide 
such details in the reader__read_event function.

Of course, I can move setting of active_decomp outside of 
reader__read_event if this is better from your point of view.

Regards,
Alexey

> 
> jirka
> 
>>
>> Regards,
>> Alexey
>>
>>>
>>> In this patch I separates single event reading and moves setting/resetting
>>> of active_decomp before/after perf_session__process_event because this is 
>>> necessary for multiple trace reader. 
>>>
>>> Regards,
>>> Alexey
>>>
>>>>
>>>> jirka
>>>>
>>>>>
>>>>> Regards,
>>>>> Alexey
>>>>>
>>>>>>
>>>>>> jirka
>>>>>>
>>>>>>>  	return err;
>>>>>>>  }
>>>>>>>  
>>>>>>> -- 
>>>>>>> 2.19.0
>>>>>>>
>>>>>>
>>>>>
>>>>
>>
>