linux-kernel - Re: Re: [PATCH] base: arch_topology: Use policy->max to calculate freq

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Message-ID: <8f7397e3-4e92-c84d-9168-087967f4d683@arm.com>
Date:   Wed, 17 Nov 2021 10:46:23 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: Re: [PATCH] base: arch_topology: Use policy->max to calculate
 freq_factor

Hi Rafael,

On 11/16/21 7:05 PM, Rafael J. Wysocki wrote:
> On Mon, Nov 15, 2021 at 9:10 PM Thara Gopinath
> <thara.gopinath@...aro.org> wrote:
>>
>> cpuinfo.max_freq can reflect boost frequency if enabled during boot.  Since
>> we don't consider boost frequencies while calculating cpu capacities, use
>> policy->max to populate the freq_factor during boot up.
> 
> I'm not sure about this.  schedutil uses cpuinfo.max_freq as the max frequency.

Agree it's tricky how we treat the boost frequencies and also combine
them with thermal pressure.
We probably would have consider these design bits:
1. Should thermal pressure include boost frequency?
2. Should max capacity 1024 be a boost frequency so scheduler
    would see it explicitly?
- if no, then schedutil could still request boost freq thanks to
   map_util_perf() where we add 25% to the util and then
   map_util_freq() would return a boost freq when util was > 1024


I can see in schedutil only one place when cpuinfo.max_freq is used:
get_next_freq(). If the value stored in there is a boost,
then don't we get a higher freq value for the same util?