Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume, aux_start_paused

From: Andi Kleen <ak@linux.intel.com>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Thomas Richter <tmricht@linux.ibm.com>,
	Hendrik Brueckner <brueckner@linux.ibm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Mike Leach <mike.leach@linaro.org>,
	James Clark <james.clark@arm.com>,
	coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
	Yicong Yang <yangyicong@hisilicon.com>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	Will Deacon <will@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
	Ian Rogers <irogers@google.com>,
	linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume, aux_start_paused
Date: Fri, 9 Feb 2024 01:49:25 -0800	[thread overview]
Message-ID: <ZcX1JUyMMpngyRqd@tassilo> (raw)
In-Reply-To: <d53ef26d-a7e6-4b3b-b593-be75425c0e77@intel.com>

On Fri, Feb 09, 2024 at 10:14:44AM +0200, Adrian Hunter wrote:
> On 9/02/24 02:13, Andi Kleen wrote:
> >> +static void __perf_event_aux_pause(struct perf_event *event, bool pause)
> >> +{
> >> +	if (pause) {
> >> +		if (!READ_ONCE(event->aux_paused)) {
> >> +			WRITE_ONCE(event->aux_paused, 1);
> >> +			event->pmu->stop(event, PERF_EF_PAUSE);
> >> +		}
> >> +	} else {
> >> +		if (READ_ONCE(event->aux_paused)) {
> >> +			WRITE_ONCE(event->aux_paused, 0);
> >> +			event->pmu->start(event, PERF_EF_RESUME);
> >> +		}
> > 
> > This doesn't look atomic. Either the READ/WRITE once are not needed,
> > or you need an actually atomic construct.
> 
> Yes READ_ONCE / WRITE_ONCE is not really needed here.

Normally you are supposed to add a comment on what the interaction
is (similar to what is done for spinlock declarations)

-Andi

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