From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF6DB2F1FF4; Mon, 22 Jun 2026 12:20:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782130817; cv=none; b=WRYvGXwo4BfJxZkzgLGpQWs+BdWl6Jf6Wn7pER+xDyX/r4JoJfA7uP2gY4dm0IJGExTq2uWdEwExAeRlVJFihIKwdC11LlVfpUuwmgmfRYLbgYhuNwG/k4giCtm7ZuRrxNo7ZLYcc5whlhf19IOibbQr8qA1c+Bo/T0yS88mVIk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782130817; c=relaxed/simple; bh=OrQXfx7uDMhRKWVSEdkG0//atS5bKeZfGc7UyIlpxqY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JH9vaWxxYfh3lkq5LqJKUDKNad24fCemB/9xj1T0B2bf2D17f8wyrIIwnd3u7lXmBE6IlzCjhgspWqB1NUdjvN5q51QZmTAXUNlf7JqjNyC+9UAX39VuXtDfqG5WNknVnOAJL4xjaKVkl8yaK2zvfYj9ZDpDwKyMZwWDX1kaHuk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=luy7boXg; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="luy7boXg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB6F11F000E9; Mon, 22 Jun 2026 12:20:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782130815; bh=z+jtKgtQRID1XboOt93fMS9cJd+U+n9q6G3fzyc6a1M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=luy7boXgMRCgMq/tUfI1wfzfmcive9UU4DJ19R0fpFwYoTGnBsq5p3nIGX0jldpNc K/c9+uIFkBZ2omHr3NfuqAtxFqEZN0jOM7dZ9zTcuiGyCcqlc3d3vrBY+1RRJed3hN mmk5vfNWLv/rYyQ8H0qL4YECc+9MbWqyAcSvZvmQXn/fqcPFrvKJMNLkmec8T5txn3 8DY/Rz+CW0FFmcgT/+lFVsKiId+KAayti49xdhx5dbmNbctn8GZqnzf10H//k2Cj+z gC1VZdvIlST0XPAf5x2PnBGkx3FJ/yHGvurnCBNWbPnrLfLSjLf94IX0ZCuyGoYk6V Meo+f/Q8gtkPg== Message-ID: Date: Mon, 22 Jun 2026 14:20:07 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 00/31] Introduce SCMI Telemetry FS support To: Cristian Marussi Cc: Christian Brauner , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, arm-scmi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, sudeep.holla@kernel.org, james.quinlan@broadcom.com, f.fainelli@gmail.com, vincent.guittot@linaro.org, etienne.carriere@st.com, peng.fan@oss.nxp.com, michal.simek@amd.com, d-gole@ti.com, jic23@kernel.org, elif.topuz@arm.com, lukasz.luba@arm.com, philip.radford@arm.com, souvik.chakravarty@arm.com, leitao@kernel.org, kas@kernel.org, puranjay@kernel.org, usama.arif@linux.dev, kernel-team@meta.com References: <20260612223802.1337232-1-cristian.marussi@arm.com> <20260617-waten-allabendlich-zueinander-93d4b1367b8c@brauner> <29a304f0-1e62-418a-b84f-aabdc4c0de8d@kernel.org> <0025b907-27b9-4a51-b78f-f8ad413644d0@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit >>> >>> There is more stuff that indeed is configurable per the SCMI spec >>> but these additional params are hidden into the SCMI Telemetry protocol >>> layer (the initial patches in this series) and NOT made available to >>> the driver/users of the protocol (like the SCMI FS driver that sits on >>> top) >> >> Do you assume that there will get significantly more config options added in the >> future for user space to configure? > > No, I dont think so...the only planned extensions were to support more > performant read access mechanisms, i.e. direct mmap'ability of FW/Kernel > SCMI Telemetry shared memory areas...BUT that will immediately dump all > the bulk of the lower layer protocol work into the tools domain...and Right. I guess you would hide that in library code, and provide a stable API towards tools such that they won't have to worry about the implementation details regarding how the values are obtained exactly. [...] >>> >>> ...most of the other entries in the tree are simply RO properties of the DEs >>> that have been discovered at enumeration time. >> >> Is this bulk-reading relevant for performance or just a "nice to have" ? >> > > I suppose depends on your usage pattern: it is definitely relevant > because the main collection mechanism are shared memory areas (SHMTIs) > between the platform firmware and the Kernel: such areas being accessed > from 2 differnt worlds concurrently come with a SCMI-specified > synchro/consistency mechanism based simply on a pair of sequence numbers > placed at the start and at the end of the SHMTI, so that the FW increases > such magic numbers in a well-known way before and after updating the SHMTI > values, so that the kernel can detect (without any interlocking mechanism) > if a platform write happened in the middle of its reads... Okay, so sequence counters to detect concurrent changes and retry. > > ...so if you read one single DE 64bit value, under the hood the kernel > would have had to really perform at leats 3 reads from the SHMTI to check > the consistecy of that single read... > > ... while if you do a bulk_read the overhead due to the consistecy > checks gets 'spread' across a number of DEs because the kernel will snapshot > the whole SHMTIs (potentially KBytes) between the 2 consistency reads That makes sense. I guess a user space library could implement some kind of caching (bulk-read, then provide clean access to individual DEs) to hide the details from the tools? > > ...the good side effect of all of this is that I can leverage such > sequence number to optimize reads..i.e. do NOT even try to read anything > if the new sequnce number is unchanged from the last one I cached on the > last successfull read of this value... Right. > > So at the end I would say it is NOT simply a nice to have BUT it is > certainly only the first step towards a more performant alternative access > (like with mmaps)...it depends on the usage pattern...I am not sure what > mechanism is used by our tools more... Okay. >> >> Yes. How high-priority is the fs side? Or would a tool using a library to access >> this information also work in the first step? >> > > I have to sync with tools on this...because they are stiil probably > using currently the FS, but it was already planned for the future to move to > a more low level access (ioctl/mmap)... > > ...my aim would be, at this point, to favour this transition without sudden > breaking their current world (and have to expatriate :P) > > ..from my personal point of view, I would certainly like to still have the > FUSE layer for ease of testing and verification on my side...but it is just > a nice to have... Okay, what I thought. I assume the most important part is to be able to grab telemetry data in an efficient way on a system to then share it with some monitoring agent. Manually digging through the FS to inspect data (debugging, ..) is probably less relevant for the target use case. >> Okay, so a single writer (admin) changing stuff could get picked up my possibly >> many concurrent readers? > > Mmm...not sure what you mean here... > > If you configure your Telemetry as you desire and start collecting data via > readers, BUT then some other process changes configs under your belt, that is > allowed as said, and so your analisys could be impacted...(something turned off > as an example, or update interval changed)... I was rather wondering about "turning on more" concurrently. But yeah, makes sense. (it's the same situation other system-wide settings. If one app enables KSM and the another one disables KSM, inconsistency is unavoidable) >> > > Thanks a lot, David ! Let's hope for some guidance regarding the FS side soon. But yeah, avoiding the in-kernel FS sounds completely reasonable at this point. -- Cheers, David