From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com> To: Viresh Kumar <viresh.kumar@linaro.org>, Beata Michalska <beata.michalska@arm.com> Cc: 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: Re: [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq Date: Wed, 1 May 2024 07:46:26 -0700 [thread overview] Message-ID: <sjm6ktvjql5ce5icfqaxlwvql2jchpya6pgtr6jkjiodztpcno@p5kse5mwqwbl> (raw) In-Reply-To: <20240429092515.2ehk4ifcul6mbaxh@vireshk-i7> 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 ? I had the same concerns. It probably makes sense explicity note this in the next version of the patch series; in the future readers may be confused by x86 and ARM behave differntly on scaling_cur_freq. Thanks, Vanshi > >-- >viresh
WARNING: multiple messages have this Message-ID (diff)
From: Vanshidhar Konda <vanshikonda@os.amperecomputing.com> To: Viresh Kumar <viresh.kumar@linaro.org>, Beata Michalska <beata.michalska@arm.com> Cc: 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: Re: [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq Date: Wed, 1 May 2024 07:46:26 -0700 [thread overview] Message-ID: <sjm6ktvjql5ce5icfqaxlwvql2jchpya6pgtr6jkjiodztpcno@p5kse5mwqwbl> (raw) In-Reply-To: <20240429092515.2ehk4ifcul6mbaxh@vireshk-i7> 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 ? I had the same concerns. It probably makes sense explicity note this in the next version of the patch series; in the future readers may be confused by x86 and ARM behave differntly on scaling_cur_freq. Thanks, Vanshi > >-- >viresh _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-05-01 14:46 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-04-05 13:33 [PATCH v4 0/4] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu Beata Michalska 2024-04-05 13:33 ` Beata Michalska 2024-04-05 13:33 ` [PATCH v4 1/4] arch_topology: init capacity_freq_ref to 0 Beata Michalska 2024-04-05 13:33 ` Beata Michalska 2024-04-08 8:35 ` Vincent Guittot 2024-04-08 8:35 ` Vincent Guittot 2024-04-05 13:33 ` [PATCH v4 2/4] arm64: Provide an AMU-based version of arch_freq_get_on_cpu Beata Michalska 2024-04-05 13:33 ` Beata Michalska 2024-04-05 13:33 ` [PATCH v4 3/4] arm64: Update AMU-based frequency scale factor on entering idle Beata Michalska 2024-04-05 13:33 ` Beata Michalska 2024-04-10 18:57 ` Sumit Gupta 2024-04-10 18:57 ` Sumit Gupta 2024-04-11 19:30 ` Beata Michalska 2024-04-11 19:30 ` Beata Michalska 2024-04-05 13:33 ` [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq Beata Michalska 2024-04-05 13:33 ` Beata Michalska 2024-04-16 4:23 ` Vanshidhar Konda 2024-04-16 4:23 ` Vanshidhar Konda 2024-04-16 15:46 ` Beata Michalska 2024-04-16 15:46 ` Beata Michalska 2024-04-17 21:38 ` Vanshidhar Konda 2024-04-17 21:38 ` Vanshidhar Konda 2024-04-26 10:45 ` Beata Michalska 2024-04-26 10:45 ` Beata Michalska 2024-04-29 9:25 ` Viresh Kumar 2024-04-29 9:25 ` Viresh Kumar 2024-05-01 14:46 ` Vanshidhar Konda [this message] 2024-05-01 14:46 ` Vanshidhar Konda 2024-05-07 8:31 ` Beata Michalska 2024-05-07 8:31 ` Beata Michalska 2024-05-07 10:02 ` Beata Michalska 2024-05-07 10:02 ` Beata Michalska 2024-05-20 9:18 ` Viresh Kumar 2024-05-20 9:18 ` Viresh Kumar
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