linux-kernel - Re: [PATCH V2 22/30] coresight: etm-perf: new PMU driver for ETM tracers

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Message-ID: <CANLsYkxk6shqkqd6Omzo5J4zeeSJ-uxhk0MDdiQ3mrmGmmBFpQ@mail.gmail.com>
Date:	Tue, 20 Oct 2015 10:43:14 -0600
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>, a.p.zijlstra@...llo.nl,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, Jon Corbet <corbet@....net>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	Mike Leach <mike.leach@....com>,
	"Jeremiassen, Tor" <tor@...com>, Al Grant <al.grant@....com>,
	Paweł Moll <pawel.moll@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 22/30] coresight: etm-perf: new PMU driver for ETM tracers

On 19 October 2015 at 09:37, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Mathieu Poirier <mathieu.poirier@...aro.org> writes:
>
>> +static int etm_event_pmu_start(struct perf_event *event)
>> +{
>> +     int cpu, ret;
>> +     cpumask_t mask;
>> +     struct coresight_device *csdev;
>> +
>> +     cpumask_clear(&mask);
>> +     if (event->cpu != -1)
>> +             cpumask_set_cpu(event->cpu, &mask);
>> +     else
>> +             cpumask_copy(&mask, cpu_online_mask);
>> +
>> +     for_each_cpu(cpu, &mask) {
>> +             csdev = per_cpu(csdev_src, cpu);
>> +
>> +             if (!source_ops(csdev)->perf_start)
>> +                     continue;
>> +
>> +             ret = source_ops(csdev)->perf_start(csdev);
>> +             if (ret)
>> +                     goto err;
>
> So long as "perf_start" and "perf_stop" here mean
> "pm_runtime_get()/put()", this can work, but in that case maybe a better
> name should be used, because no real starting or stopping of anything
> takes place here.

You're correct, nothing else than pm_runtime operations should be
happening in there.  I will revise the naming convention.

> Since pmu::event_init and event::destroy happen in
> allocation/deallocation paths and at event scheduling, it's not a good
> idea to actually start anything here.
>
> Regards,
> --
> Alex
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