From nobody Fri Jan 2 17:10:55 2026 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 2BC3BCD80A2 for ; Tue, 10 Oct 2023 10:42:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231184AbjJJKmT (ORCPT ); Tue, 10 Oct 2023 06:42:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231216AbjJJKmO (ORCPT ); Tue, 10 Oct 2023 06:42:14 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id F222DC4; Tue, 10 Oct 2023 03:42:11 -0700 (PDT) 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 6CCA91FB; Tue, 10 Oct 2023 03:42:52 -0700 (PDT) Received: from localhost.localdomain (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3C2A83F762; Tue, 10 Oct 2023 03:42:09 -0700 (PDT) From: James Clark To: linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, suzuki.poulose@arm.com Cc: James Clark , Catalin Marinas , Will Deacon , Jonathan Corbet , Russell King , Marc Zyngier , Oliver Upton , James Morse , Zenghui Yu , Mark Rutland , Geert Uytterhoeven , Reiji Watanabe , Zaid Al-Bassam , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev Subject: [PATCH v2 3/3] Documentation: arm64: Document the PMU event counting threshold feature Date: Tue, 10 Oct 2023 11:40:29 +0100 Message-Id: <20231010104048.1923484-4-james.clark@arm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231010104048.1923484-1-james.clark@arm.com> References: <20231010104048.1923484-1-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 two new Perf event open parameters and the threshold_max capability file. Signed-off-by: James Clark --- Documentation/arch/arm64/perf.rst | 58 +++++++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) diff --git a/Documentation/arch/arm64/perf.rst b/Documentation/arch/arm64/p= erf.rst index 1f87b57c2332..122a12607f37 100644 --- a/Documentation/arch/arm64/perf.rst +++ b/Documentation/arch/arm64/perf.rst @@ -164,3 +164,61 @@ 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_control is set to 5 ('Greater than or equal, count'), and +the threshold is set to 2, then the PMU counter will now only increment +by 1 when an event would have previously incremented the PMU counter by +2 or more on a single processor cycle. + +To increment by the value of the event instead of 1, use the non 'count' +comparisons, in this case 4 ('Greater than or equal'). Each comparison +has a count and non count version, where the 'count' version always +increments the PMU counter by 1 instead of the value of the event. + +How-to +------ + +The threshold and threshold control values can be provided per event: + +.. code-block:: sh + + perf stat -e stall_slot/threshold=3D2,threshold_control=3D5/ \ + -e dtlb_walk/threshold=3D10,threshold_control=3D4/ + +And the following control values are supported: + +.. code-block:: + + 0: Not-equal + 1: Not-equal, count + 2: Equals + 3: Equals, count + 4: Greater-than-or-equal + 5: Greater-than-or-equal, count + 6: Less-than + 7: Less-than, count + +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_control will be silently ignored. --=20 2.34.1