From patchwork Mon Dec 11 16:13:23 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: James Clark X-Patchwork-Id: 13487513 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 43521186; Mon, 11 Dec 2023 08:16:09 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 877CE16F2; Mon, 11 Dec 2023 08:16:55 -0800 (PST) Received: from e127643.broadband (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 1313D3F738; Mon, 11 Dec 2023 08:16:04 -0800 (PST) From: James Clark To: linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, suzuki.poulose@arm.com, will@kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com Cc: namhyung@gmail.com, James Clark , Namhyung Kim , Catalin Marinas , Jonathan Corbet , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Russell King , Marc Zyngier , Oliver Upton , James Morse , Zenghui Yu , Paolo Bonzini , Shuah Khan , Zaid Al-Bassam , Raghavendra Rao Ananta , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v7 11/11] Documentation: arm64: Document the PMU event counting threshold feature Date: Mon, 11 Dec 2023 16:13:23 +0000 Message-Id: <20231211161331.1277825-12-james.clark@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231211161331.1277825-1-james.clark@arm.com> References: <20231211161331.1277825-1-james.clark@arm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Add documentation for the new Perf event open parameters and the threshold_max capability file. Reviewed-by: Anshuman Khandual Reviewed-by: Suzuki K Poulose Acked-by: Namhyung Kim Signed-off-by: James Clark --- Documentation/arch/arm64/perf.rst | 72 +++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) diff --git a/Documentation/arch/arm64/perf.rst b/Documentation/arch/arm64/perf.rst index 1f87b57c2332..997fd716b82f 100644 --- a/Documentation/arch/arm64/perf.rst +++ b/Documentation/arch/arm64/perf.rst @@ -164,3 +164,75 @@ and should be used to mask the upper bits as needed. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm64/tests/user-events.c .. _tools/lib/perf/tests/test-evsel.c: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/perf/tests/test-evsel.c + +Event Counting Threshold +========================================== + +Overview +-------- + +FEAT_PMUv3_TH (Armv8.8) permits a PMU counter to increment only on +events whose count meets a specified threshold condition. For example if +threshold_compare is set to 2 ('Greater than or equal'), and the +threshold is set to 2, then the PMU counter will now only increment by +when an event would have previously incremented the PMU counter by 2 or +more on a single processor cycle. + +To increment by 1 after passing the threshold condition instead of the +number of events on that cycle, add the 'threshold_count' option to the +commandline. + +How-to +------ + +These are the parameters for controlling the feature: + +.. list-table:: + :header-rows: 1 + + * - Parameter + - Description + * - threshold + - Value to threshold the event by. A value of 0 means that + thresholding is disabled and the other parameters have no effect. + * - threshold_compare + - | Comparison function to use, with the following values supported: + | + | 0: Not-equal + | 1: Equals + | 2: Greater-than-or-equal + | 3: Less-than + * - threshold_count + - If this is set, count by 1 after passing the threshold condition + instead of the value of the event on this cycle. + +The threshold, threshold_compare and threshold_count values can be +provided per event, for example: + +.. code-block:: sh + + perf stat -e stall_slot/threshold=2,threshold_compare=2/ \ + -e dtlb_walk/threshold=10,threshold_compare=3,threshold_count/ + +In this example the stall_slot event will count by 2 or more on every +cycle where 2 or more stalls happen. And dtlb_walk will count by 1 on +every cycle where the number of dtlb walks were less than 10. + +The maximum supported threshold value can be read from the caps of each +PMU, for example: + +.. code-block:: sh + + cat /sys/bus/event_source/devices/armv8_pmuv3/caps/threshold_max + + 0x000000ff + +If a value higher than this is given, then opening the event will result +in an error. The highest possible maximum is 4095, as the config field +for threshold is limited to 12 bits, and the Perf tool will refuse to +parse higher values. + +If the PMU doesn't support FEAT_PMUv3_TH, then threshold_max will read +0, and attempting to set a threshold value will also result in an error. +threshold_max will also read as 0 on aarch32 guests, even if the host +is running on hardware with the feature.