From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AACBB303A19; Wed, 26 Nov 2025 14:44:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764168282; cv=none; b=OjO3UPV8C06hebZCUI1aW6m5VsDphZ4NBQC9VSkZ3N2DDqEwUNhhBRLeipBj1CoSzDYPLSJTx8hGac4Ndtlx8yCwyKhH3GGBFNqFmas3hwJHiXEL6raFsD5Rld6yG5LzwPBvT6alVLtOTa90+sHUqF6EfX5ngjQN38nZT7ZYTIs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764168282; c=relaxed/simple; bh=2cppOkVKgl0pjKR1U/CqP0UN6xPwA2lHW16XyELe1JI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KB6LZwcTxMYB+BU80x5kB3oN3pAHv21+NImAmVMnx+NxhMjXx+klCnITl+kuCLHEDCx/u042zU1nu6P+vRNrg8n/1RUZeBdY0Ll+/ZxcqppHwhsLcZxZ5TYC0oZGmqH2KfXtP94K9W0uTd0hdxi0Ubmqu8gru8uQqdLFAVq+QDk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 882F9168F; Wed, 26 Nov 2025 06:44:32 -0800 (PST) Received: from localhost (e132581.arm.com [10.1.196.87]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8FFB53F73B; Wed, 26 Nov 2025 06:44:39 -0800 (PST) Date: Wed, 26 Nov 2025 14:44:37 +0000 From: Leo Yan To: Mike Leach Cc: James Clark , Suzuki K Poulose , Alexander Shishkin , Jonathan Corbet , Randy Dunlap , coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v7 13/13] coresight: docs: Document etm4x timestamp interval option Message-ID: <20251126144437.GL724103@e132581.arm.com> References: <20251126-james-cs-syncfreq-v7-0-7fae5e0e5e16@linaro.org> <20251126-james-cs-syncfreq-v7-13-7fae5e0e5e16@linaro.org> <20251126140154.GK724103@e132581.arm.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Nov 26, 2025 at 02:20:14PM +0000, Mike Leach wrote: [...] > > > * - timestamp > > > - - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP > > > - ` > > > + - Controls generation and interval of timestamps. > > > + > > > + 0 = off, 1 = minimum interval .. 15 = maximum interval. > > > + > > > + Values 1 - 14 use a counter that decrements every cycle to generate a > > > + timestamp on underflow. The reload value for the counter is 2 ^ (interval > > > + - 1). If the value is 1 then the reload value is 1, if the value is 11 > > > + then the reload value is 1024 etc. > > > + > > > + Setting the maximum interval (15) will disable the counter generated > > > + timestamps, freeing the counter resource, leaving only ones emitted when > > > + a SYNC packet is generated. The sync interval is controlled with > > > + TRCSYNCPR.PERIOD which is every 4096 bytes of trace by default. > > > + > > What is the default value? >From driver's pespective, the default value is 0 (disabled). We do set default values in perf: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/arch/arm/util/cs-etm.c#n444 IIUC, the default value would be the same with or without this series. > As far as I recall when this command line parameter was a bool then: > perf -e cs_etm/timestamp/ > is sufficient to turn on timestamping. Hmm... with the latest perf, we must assign value to `timestamp`, otherwise perf will report error: # /mnt/build/perf record -e cs_etm/timestamp/ -C 0 -- taskset -c 0 ls event syntax error: 'cs_etm/timestamp/' \___ Bad event or PMU Unable to find PMU or event on a PMU of 'cs_etm' event syntax error: 'cs_etm/timestamp/' \___ no value assigned for term event syntax error: 'cs_etm/timestamp/' \___ no value assigned for term Run 'perf list' for a list of valid events > This is worth mentioning so users can correctly assess what happens > for any existing scripts they might have. > > Based on this then the same command must set the timestamp to 1 - > which will have the same effect as before as we do not want to break > existing behaviour. > > Mike > > > > > * - cc_threshold > > > - Cycle count threshold value. If nothing is provided here or the provided value is 0, then the > > > default value i.e 0x100 will be used. If provided value is less than minimum cycles threshold > > > > > > -- > > > 2.34.1 > > > > > > > -- > Mike Leach > Principal Engineer, ARM Ltd. > Manchester Design Centre. UK