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

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Date:   Mon, 11 Oct 2021 15:21:19 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Bayduraev, Alexey V" <alexey.v.bayduraev@...ux.intel.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 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

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
> >>>>>
> >>>>
> >>>
> >>
>