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 7EE6014D6EB for ; Tue, 7 May 2024 10:02:54 +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=1715076178; cv=none; b=GQtcSUncZTFMF6lMjaiAcFEhO/2kSXNxCil5fbdvXkXE7xEhY4AGTs58gAmWlzPtriNPp0ILFXTnkKreVeIEQPCha+IYseXfctY7xo5UI0MmrxxVnL8q6zmz7uuSwdyd3qO0kdyTxREozg/+ECgjQulzGr6E1VJpBjET60TC1zc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1715076178; c=relaxed/simple; bh=7Kis4nEEBzRiFLLc4dkS5IjPowhggqwv8B/amQlzr2g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tGB2+EsPQlmME8/P1x01yq0Om5kb1Zjv1tGZq2UeX2tTGk1XX1ekSsausYckZS7NpSOA+HrWZ+lmWOI4QyHDGtUCYxZVw1AClfvniLR0dAardopJ1rRWQaLvT00fiXieMZX7lvQFhBJCKYRIxGvJyVlHv70sdWdlJnsbSsZHb1M= 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 7EDCA1063; Tue, 7 May 2024 03:03:20 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2771C3F587; Tue, 7 May 2024 03:02:51 -0700 (PDT) Date: Tue, 7 May 2024 12:02:44 +0200 From: Beata Michalska To: Viresh Kumar Cc: Vanshidhar Konda , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ionela.voinescu@arm.com, sudeep.holla@arm.com, will@kernel.org, catalin.marinas@arm.com, vincent.guittot@linaro.org, sumitg@nvidia.com, yang@os.amperecomputing.com, lihuisong@huawei.com Subject: Re: [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq Message-ID: References: <20240405133319.859813-1-beata.michalska@arm.com> <20240405133319.859813-5-beata.michalska@arm.com> <76zutrz47zs6i2cquvjo2qn7myxpq7e3c6alhper7n3wrkhf5h@22l5t5pio2cd> <20240429092515.2ehk4ifcul6mbaxh@vireshk-i7> Precedence: bulk X-Mailing-List: linux-kernel@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 Tue, May 07, 2024 at 10:31:52AM +0200, Beata Michalska wrote: > On Mon, Apr 29, 2024 at 02:55:15PM +0530, Viresh Kumar wrote: > > On 26-04-24, 12:45, Beata Michalska wrote: > > > It seems that we might need to revisit the discussion we've had around > > > scaling_cur_freq and cpuinfo_cur_freq and the use of arch_freq_get_on_cpu. > > > As Vanshi has raised, having both utilizing arch specific feedback for > > > getting current frequency is bit problematic and might be confusing at best. > > > As arch_freq_get_on_cpu is already used by show_scaling_cur_freq there are not > > > many options we are left with, if we want to kee all archs aligned: > > > we can either try to rework show_scaling_cur_freq and it's use of > > > arch_freq_get_on_cpu, and move it to cpuinfo_cur_freq, which would align with > > > relevant docs, though that will not work for x86, or we keep it only there and > > > skip updating cpuinfo_cur_freq, going against the guidelines. Other options, > > > purely theoretical, would involve making arch_freq_get_on_cpu aware of type of > > > the info requested (hw vs sw) or adding yet another arch-specific implementation, > > > and those are not really appealing alternatives to say at least. > > > What's your opinion on this one ? > > > > Hi Beata / Vanshidhar, > > > > Lets forget for once what X86 and ARM may have done and think about it > > once again. I also had a chat with Vincent today about this. > > > > The documentation says it clearly, cpuinfo_cur_freq is the one > > received from hardware and scaling_cur_freq is the one requested from > > software. > > > > Now, I know that X86 has made both of them quite similar and I > > suggested to make them all aligned (and never received a reply on my > > previous message). > > > > There are few reasons why it may be worth keeping the definition (and > > behavior) of the sysfs files as is, at least for ARM: > > - First is that the documentation says so. > > - There is no point providing the same information via both the > > interfaces, there are two interfaces here for a reason. > > - There maybe tools around which depend on the documented behavior. > > - From userspace, currently there is only one way to know the exact > > frequency that the cpufreq governors have requested from a platform, > > i.e. the value from scaling_cur_freq. If we make it similar to > > cpuinfo_cur_freq, then userspace will never know about the requested > > frequency and the eventual one and if they are same or different. > > > > Lets keep the behavior as is and update only cpuinfo_cur_freq with > > arch_freq_get_on_cpu(). > > > > Makes sense ? > > > First of all - apologies for late reply. > > It all makes sense, though to clarify things up, for my own benefit, and to > avoid any potential confusion .... > > Adding arch_freq_get_on_cpu to cpuinfo_cur_freq does seem to be the right > approach - no argue on this one. Doing that though means we need a way to > skip calling arch_freq_get_on_cpu() from show_scaling_cur_freq(), to avoid > having both providing the same information when that should not be the case. > In the initial approach [1], that was handled by checking whether the cpufreq > driver supports 'get' callback (and thus cpuinfo_cur_freq). In case it didn't, > things remained unchanged for scaling_cur_freq. That does not seem to be a viable > option though, as there are at least few drivers, that will support both: > cpuinfo_cur_freq alongside scaling_cur_freq (+ APERF/MPERF) and for those, > we would hit the initial problem of both relying on arch_freq_get_on_cpu. > So I guess we need another way of avoiding calling arch_freq_get_on_cpu > for show_scaling_cur_freq (and most probably avoid calling that one for > cpuinfo_cur_freq). Quick idea on how to not bring arch specificity into > cpufreq generic code would be to introduce a new flag for cpufreq drivers though > that seems a bit stretched. Will ponder a bit about that but in the meantime > suggestions are more than welcomed. Alternatively we could add a parameter to arch_freq_get_on_cpu specifying type of feedback required: hw vs sw. Then the arch specific implementation could decide which to provide when. It will get slightly counter-intuitive, especially for cases when sw feedback provides hw one, as it is the case for current arch_freq_get_on_cpu() and scaling_cur_freq but at least the changes would be minimal and it will contain handling the tricky bits inside arch specific implementation - hiding those messy bits. --- BR Beata > > Aside: I will most probably send the changes separately from this series to not > mix things any further. > > --- > [1] https://lore.kernel.org/all/20230606155754.245998-1-beata.michalska@arm.com/ > --- > BR > Beata > > > > -- > > viresh