linux-kernel - Re: [PATCH v2 02/14] perf mem: Introduce weak function perf_mem_events_

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Date:   Fri, 4 Sep 2020 17:52:51 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Kemeng Shi <shikemeng@...wei.com>,
        James Clark <james.clark@....com>,
        Wei Li <liwei391@...wei.com>, Al Grant <Al.Grant@....com>,
        Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/14] perf mem: Introduce weak function
 perf_mem_events__ptr()

On Fri, Sep 04, 2020 at 08:34:47AM +0800, Leo Yan wrote:
> Hi Jiri,
> 
> On Thu, Sep 03, 2020 at 03:50:54PM +0200, Jiri Olsa wrote:
> > On Tue, Sep 01, 2020 at 09:38:03AM +0100, Leo Yan wrote:
> > 
> > SNIP
> > 
> > > @@ -2941,30 +2942,38 @@ static int perf_c2c__record(int argc, const char **argv)
> > >  	rec_argv[i++] = "record";
> > >  
> > >  	if (!event_set) {
> > > -		perf_mem_events[PERF_MEM_EVENTS__LOAD].record  = true;
> > > -		perf_mem_events[PERF_MEM_EVENTS__STORE].record = true;
> > > +		e = perf_mem_events__ptr(PERF_MEM_EVENTS__LOAD);
> > > +		e->record = true;
> > > +
> > > +		e = perf_mem_events__ptr(PERF_MEM_EVENTS__STORE);
> > > +		e->record = true;
> > >  	}
> > >  
> > > -	if (perf_mem_events[PERF_MEM_EVENTS__LOAD].record)
> > > +	e = perf_mem_events__ptr(PERF_MEM_EVENTS__LOAD);
> > > +	if (e->record)
> > >  		rec_argv[i++] = "-W";
> > >  
> > >  	rec_argv[i++] = "-d";
> > >  	rec_argv[i++] = "--phys-data";
> > >  	rec_argv[i++] = "--sample-cpu";
> > >  
> > > -	for (j = 0; j < PERF_MEM_EVENTS__MAX; j++) {
> > > -		if (!perf_mem_events[j].record)
> > > +	j = 0;
> > > +	while ((e = perf_mem_events__ptr(j)) != NULL) {
> > > +		if (!e->record) {
> > 
> > you could keep the above 'for loop' in here, it seems better
> > than taking care of j++
> 
> Actually in patch v1 I did this way :)  I followed James' suggestion to
> encapsulate PERF_MEM_EVENTS__MAX into perf_mem_events__ptr(), thus
> builtin-mem.c and buildin-c2c.c are not necessary to use
> PERF_MEM_EVENTS__MAX in the loop and only needs to detect if the
> pointer is NULL or not when return from perf_mem_events__ptr().

ah because u added that load_store event

> 
> How about change as below?
> 
>         for (j = 0; (e = perf_mem_events__ptr(j)) != NULL; j++) {
>                 [...]

will this work? e will be NULL for first iteration no?

there are still other for loops with PERF_MEM_EVENTS__MAX used
in the patch.. you overload the perf_mem_events access for arm,
and add missing load_store NULL item to generic version, so there's
always PERF_MEM_EVENTS__MAX items in the array

can we just use the current for loop and check for e->tag != NULL
or any other field

thanks,
jirka