From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=none Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 8080E1727; Fri, 24 Nov 2023 01:52:03 -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 B2E591063; Fri, 24 Nov 2023 01:52:49 -0800 (PST) Received: from [192.168.1.3] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E34173F7A6; Fri, 24 Nov 2023 01:52:01 -0800 (PST) Message-ID: Date: Fri, 24 Nov 2023 09:52:00 +0000 Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH v5 3/3] Documentation: arm64: Document the PMU event counting threshold feature From: James Clark To: Anshuman Khandual , Namhyung Kim Cc: linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, suzuki.poulose@arm.com, will@kernel.org, mark.rutland@arm.com, Catalin Marinas , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20231113112507.917107-1-james.clark@arm.com> <20231113112507.917107-4-james.clark@arm.com> <0bcda96e-df9a-4342-af4e-e4485c33ff55@arm.com> <4f959354-74c7-5240-bf8f-78a49fb34437@arm.com> Content-Language: en-US In-Reply-To: <4f959354-74c7-5240-bf8f-78a49fb34437@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 23/11/2023 15:45, James Clark wrote: > > > On 23/11/2023 05:50, Anshuman Khandual wrote: >> >> >> On 11/21/23 03:01, Namhyung Kim wrote: >>> On Mon, Nov 13, 2023 at 3:26 AM James Clark wrote: >>>> Add documentation for the new Perf event open parameters and >>>> the threshold_max capability file. >>>> >>>> Signed-off-by: James Clark >>>> --- >>>> Documentation/arch/arm64/perf.rst | 56 +++++++++++++++++++++++++++++++ >>>> 1 file changed, 56 insertions(+) >>>> >>>> diff --git a/Documentation/arch/arm64/perf.rst b/Documentation/arch/arm64/perf.rst >>>> index 1f87b57c2332..36b8111a710d 100644 >>>> --- a/Documentation/arch/arm64/perf.rst >>>> +++ b/Documentation/arch/arm64/perf.rst >>>> @@ -164,3 +164,59 @@ 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 >>>> +------ >>>> + >>>> +The threshold, threshold_compare and threshold_count values can be >>>> +provided per event: >>>> + >>>> +.. code-block:: sh >>>> + >>>> + perf stat -e stall_slot/threshold=2,threshold_compare=2/ \ >>>> + -e dtlb_walk/threshold=10,threshold_compare=3,threshold_count/ >>> Can you please explain this a bit more? >>> >>> I guess the first event counts stall_slot PMU if the event if it's >>> greater than or equal to 2. And as threshold_count is not set, >>> it'd count the stall_slot as is. E.g. it counts 3 when it sees 3. >> >> Hence without 'threshold_count' being set, the other two config requests >> will not have an effect, is that correct ? > > Yeah I can mention this. It's implied because 0 is the default value of > config fields, and 0 is a valid value for compare and count field, so > threshold=0 has to be the way to disable it. But I can mention it > explicitly. > To avoid any confusion, I thought you meant threshold here instead of threshold_count. But I replied in more detail about the same issue on patch 2.