linux-kernel - Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

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Message-ID: <5172dfcb-2d4c-6f90-671c-bd3639b44aab@arm.com>
Date:   Thu, 13 Jul 2017 15:06:12 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Juri Lelli <juri.lelli@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant
 load-tracking support



On 13/07/17 14:08, Dietmar Eggemann wrote:
> On 13/07/17 13:40, Sudeep Holla wrote:
>>
>>
>> On 11/07/17 16:21, Dietmar Eggemann wrote:
>>> On 11/07/17 07:39, Viresh Kumar wrote:
>>>> On 10-07-17, 14:46, Rafael J. Wysocki wrote:
> 
> [...]
> 
>>> Like I said in the other email, since for (future)
>>> arm/arm64 fast-switch driver, the return value of
>>> cpufreq_driver->fast_switch() does not give us the information that the
>>> frequency value did actually change, we have to implement
>>
>> I was under the impression that we strictly don't care about that
>> information when I started exploring the fast_switch with the standard
>> firmware interface on ARM platforms(until if and when ARM provides an
>> instruction to achieve that).
>>
>> If f/w failed to change the frequency, will that be not corrected in the
>> next sample or instance. I would like to know the impact of absence of
>> such notifications.
> 
> In the meantime we agreed that we have to invoke frequency invariance
> from within the cpufreq driver.
> 
> For a fast-switch driver I would have to put the call to
> arch_set_freq_scale() somewhere where I know that the frequency has been
> set.
> 
> Without a notification (from the firmware) that the frequency has been
> set, I would have to call arch_set_freq_scale() somewhere in the
> driver::fast_switch() call assuming that the frequency has been actually
> set.
> 

Yes, that's what I was thinking too.

-- 
Regards,
Sudeep