From patchwork Fri Nov 24 10:28:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: James Clark X-Patchwork-Id: 13467496 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 44262C61DF4 for ; Fri, 24 Nov 2023 10:32:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=jkmGEQ0jFbPz2zjlBwuYOHceO+OHfKXYDB/Yuoib0+I=; b=WeLmaruWc1IPFB RSvjSNnDIWGiVdZrS6+BtTzHSB/JWj4aJTnIGF/EQ6k5Qv05IOpcO3JqHTNLfAbe+8rQsbIuacUtr 7CVJRjwyZhkzO2uS/hygfFjxCpdBS51V2knxH5uErYOWh2d7EP8+Ux/IbQDu8R3ThxYy6pobE+GmV VSE86XLK9OgGmhbxWnwOJzYYNUY50X5NCuYat0BOH6TGA2wswjUhXMP8XWGI0yMo8RCSqcwiJ/Mw/ jflqLsaLZFtabOZgszqmww/f040v7Kvq1cAgTMApFooacVOEZonugwo7K6er7Kl2eEJsKeMonG1XB I7EWS1sqppGifFAl7tBQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r6TTk-006sBB-0D; Fri, 24 Nov 2023 10:32:08 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1r6TTV-006s24-2T for linux-arm-kernel@lists.infradead.org; Fri, 24 Nov 2023 10:31:55 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231124_023153_896101_A135E57B X-CRM114-Status: GOOD ( 16.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Add documentation for the new Perf event open parameters and the threshold_max capability file. Signed-off-by: James Clark Reviewed-by: Anshuman Khandual Acked-by: Namhyung Kim 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/perf.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 +========================================== + +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 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.