From: Adrian Hunter <adrian.hunter@intel.com>
To: Andi Kleen <ak@linux.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: Mon, 12 Feb 2024 08:43:11 +0200 [thread overview]
Message-ID: <05ac66fc-ddda-46ff-b08d-c15943c16bc1@intel.com> (raw)
In-Reply-To: <ZcaUw4xQT0VcC7IO@tassilo>
On 9/02/24 23:10, Andi Kleen wrote:
>> The writes to rb->aux_in_pause_resume must be done
>> only once. It might be possible to get away without
>> WRITE_ONCE(), but really the compiler should be informed
>> not to make assumptions.
>
> What stops the NMI from firing here?
That would be fine.
>
>>>> + if (READ_ONCE(rb->aux_in_pause_resume))
>>>> + /* Guard against NMI, NMI loses here */
>>>> + goto out_restore;
> <----------------------- NMI
That would be fine.
>>>> + WRITE_ONCE(rb->aux_in_pause_resume, 1);
From here on, the NMI will see rb->aux_in_pause_resume == 1
and do nothing, up to the point when rb->aux_in_pause_resume == 0
again.
This code is about guarding against NMI. Interrupts are
disabled, and the rb and event only operate on 1 cpu at a time.
>
>
> Even if it isn't racy it needs a clear comment.
It has a comment, but it could be more explanatory. The code
paradigm is also used in perf_pmu_snapshot_aux().
next prev parent reply other threads:[~2024-02-12 6:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-08 11:31 [PATCH V5 00/12] perf/core: Add ability for an event to "pause" or "resume" AUX area tracing Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 01/12] perf/core: Add aux_pause, aux_resume, aux_start_paused Adrian Hunter
2024-02-09 0:13 ` Andi Kleen
2024-02-09 8:14 ` Adrian Hunter
2024-02-09 9:49 ` Andi Kleen
2024-02-09 21:10 ` Andi Kleen
2024-02-12 6:43 ` Adrian Hunter [this message]
2024-02-16 9:31 ` [PATCH V6] " Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 02/12] perf/x86/intel/pt: Add support for pause / resume Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 03/12] perf/x86/intel: Do not enable large PEBS for events with aux actions or aux sampling Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 04/12] perf tools: Enable evsel__is_aux_event() to work for ARM/ARM64 Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 05/12] perf tools: Enable evsel__is_aux_event() to work for S390_CPUMSF Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 06/12] perf tools: Add aux_start_paused, aux_pause and aux_resume Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 07/12] perf tools: Add aux-action config term Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 08/12] perf tools: Parse aux-action Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 09/12] perf tools: Add missing_features for aux_start_paused, aux_pause, aux_resume Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 10/12] perf intel-pt: Improve man page format Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 11/12] perf intel-pt: Add documentation for pause / resume Adrian Hunter
2024-02-08 11:31 ` [PATCH V5 12/12] perf intel-pt: Add a test " Adrian Hunter
2024-02-09 0:16 ` Andi Kleen
2024-04-11 12:02 ` [PATCH V5 00/12] perf/core: Add ability for an event to "pause" or "resume" AUX area tracing Adrian Hunter
2024-04-24 10:39 ` Adrian Hunter
2024-05-15 12:34 ` Adrian Hunter
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