linux-kernel - Re: [RESEND PATCH v12 1/3] perf tool: arm: Refactor event list iteration in auxtrace_record_

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Message-ID: <YyHkywZUVPL3GNq8@leoy-yangtze.lan>
Date:   Wed, 14 Sep 2022 22:27:23 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     John Garry <john.garry@...wei.com>
Cc:     Yicong Yang <yangyicong@...wei.com>, acme@...nel.org,
        peterz@...radead.org, alexander.shishkin@...ux.intel.com,
        james.clark@....com, will@...nel.org, mathieu.poirier@...aro.org,
        mark.rutland@....com, suzuki.poulose@....com,
        jonathan.cameron@...wei.com, mike.leach@...aro.org,
        gregkh@...uxfoundation.org, helgaas@...nel.org,
        lorenzo.pieralisi@....com, shameerali.kolothum.thodi@...wei.com,
        mingo@...hat.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org,
        linux-perf-users@...r.kernel.org, prime.zeng@...wei.com,
        zhangshaokun@...ilicon.com, linuxarm@...wei.com,
        yangyicong@...ilicon.com, liuqi6124@...il.com
Subject: Re: [RESEND PATCH v12 1/3] perf tool: arm: Refactor event list
 iteration in auxtrace_record__init()

On Wed, Sep 14, 2022 at 02:47:43PM +0100, John Garry wrote:

[...]

> >   struct auxtrace_record
> >   *auxtrace_record__init(struct evlist *evlist, int *err)
> >   {
> > -	struct perf_pmu	*cs_etm_pmu;
> > +	struct perf_pmu	*cs_etm_pmu = NULL;
> > +	struct perf_pmu **arm_spe_pmus = NULL;
> >   	struct evsel *evsel;
> > -	bool found_etm = false;
> > +	struct perf_pmu *found_etm = NULL;
> >   	struct perf_pmu *found_spe = NULL;
> > -	struct perf_pmu **arm_spe_pmus = NULL;
> > +	int auxtrace_event_cnt = 0;
> >   	int nr_spes = 0;
> > -	int i = 0;
> >   	if (!evlist)
> >   		return NULL;
> > @@ -68,24 +84,23 @@ struct auxtrace_record
> >   	arm_spe_pmus = find_all_arm_spe_pmus(&nr_spes, err);
> >   	evlist__for_each_entry(evlist, evsel) {
> > -		if (cs_etm_pmu &&
> > -		    evsel->core.attr.type == cs_etm_pmu->type)
> > -			found_etm = true;
> > -
> > -		if (!nr_spes || found_spe)
> > -			continue;
> > -
> > -		for (i = 0; i < nr_spes; i++) {
> > -			if (evsel->core.attr.type == arm_spe_pmus[i]->type) {
> > -				found_spe = arm_spe_pmus[i];
> > -				break;
> > -			}
> > -		}
> > +		if (cs_etm_pmu && !found_etm) +			found_etm =
> > find_pmu_for_event(&cs_etm_pmu, 1, evsel);
> > +
> > +		if (arm_spe_pmus && !found_spe)
> > +			found_spe = find_pmu_for_event(arm_spe_pmus, nr_spes, evsel);
> 
> should you break if found_etm and found_spe are set? Or, indeed, error and
> return directly as we do below? Indeed, I am not sure why you even require
> auxtrace_event_cnt

I think this was my suggestion :)

We can check if both 'found_etm' and 'found_spe' are set and directly
break (and bail out) for this case.  But it would introduce more complex
checking if we connect with patch 2 with new flag 'found_ptt', something
like:

  if ((found_etm && found_spe) ||
      (found_etm && found_ptt) ||
      (found_spe && found_ptt))
      break;

This is hard for later's extension if we need to support a new auxtrace
event, so using auxtrace_event_cnt would be easier to extend more
auxtrace event on Arm platforms.

Thanks,
Leo

> >   	}
> > +
> >   	free(arm_spe_pmus);
> > -	if (found_etm && found_spe) {
> > -		pr_err("Concurrent ARM Coresight ETM and SPE operation not currently supported\n");
> > +	if (found_etm)
> > +		auxtrace_event_cnt++;
> > +
> > +	if (found_spe)
> > +		auxtrace_event_cnt++;
> > +
> > +	if (auxtrace_event_cnt > 1) {
> > +		pr_err("Concurrent AUX trace operation not currently supported\n");
> >   		*err = -EOPNOTSUPP;
> >   		return NULL;
> >   	}
>