From nobody Wed Dec 17 17:29:15 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1403EC61D97 for ; Fri, 24 Nov 2023 10:32:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345256AbjKXKcC (ORCPT ); Fri, 24 Nov 2023 05:32:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345344AbjKXKbq (ORCPT ); Fri, 24 Nov 2023 05:31:46 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 9A858110; Fri, 24 Nov 2023 02:31:52 -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 CDA071474; Fri, 24 Nov 2023 02:32:38 -0800 (PST) Received: from e127643.arm.com (unknown [10.57.5.4]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 8A1D83F7A6; Fri, 24 Nov 2023 02:31:50 -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, namhyung@gmail.com Cc: James Clark , Catalin Marinas , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 3/3] Documentation: arm64: Document the PMU event counting threshold feature Date: Fri, 24 Nov 2023 10:28:57 +0000 Message-Id: <20231124102857.1106453-4-james.clark@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231124102857.1106453-1-james.clark@arm.com> References: <20231124102857.1106453-1-james.clark@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Add documentation for the new Perf event open parameters and the threshold_max capability file. Signed-off-by: James Clark Acked-by: Namhyung Kim Reviewed-by: Anshuman Khandual Reviewed-by: Suzuki K Poulose --- Documentation/arch/arm64/perf.rst | 72 +++++++++++++++++++++++++++++++ 1 file changed, 72 insertions(+) diff --git a/Documentation/arch/arm64/perf.rst b/Documentation/arch/arm64/p= erf.rst index 1f87b57c2332..41eee68951ff 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 +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +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=3D2,threshold_compare=3D2/ \ + -e dtlb_walk/threshold=3D10,threshold_compare=3D3,threshold_co= unt/ + +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 it will be silently clamped +to the maximum. 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 both threshold and threshold_compare will be silently ignored. +threshold_max will also read as 0 on aarch32 guests, even if the host +is running on hardware with the feature. --=20 2.34.1