Messages in this thread | | | Date | Wed, 1 May 2024 07:46:26 -0700 | From | Vanshidhar Konda <> | Subject | Re: Re: [PATCH v4 4/4] cpufreq: Use arch specific feedback for cpuinfo_cur_freq |
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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
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