linux-kernel - Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency invariance

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Date:   Wed, 23 Jun 2021 08:57:46 -0400
From:   Qian Cai <quic_qiancai@...cinc.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     Rafael Wysocki <rjw@...ysocki.net>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Will Deacon <will@...nel.org>, <linux-pm@...r.kernel.org>,
        <linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH V3 0/4] cpufreq: cppc: Add support for frequency
 invariance



On 6/23/2021 12:16 AM, Viresh Kumar wrote:
> On 21-06-21, 16:48, Qian Cai wrote:
>>
>>
>> On 6/21/2021 5:19 AM, Viresh Kumar wrote:
>>> CPPC cpufreq driver is used for ARM servers and this patch series tries to
>>> provide counter-based frequency invariance support for them in the absence for
>>> architecture specific counters (like AMUs).
>>
>> Viresh, this series works fine on my quick tests so far.
> 
> Do you want me to add your Tested-by for the series ?

Viresh, I am afraid I don't feel comfortable yet. I have a few new tests in development, and will provide an update once ready. Also, I noticed the delivered perf is even smaller than lowest_perf (100).

# cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs
 ref:103377547901 del:54540736873
# cat /sys/devices/system/cpu/cpu8/acpi_cppc/feedback_ctrs
 ref:103379170101 del:54541599117

100 * (54541599117 - 54540736873) / (103379170101 - 103377547901) = 53

My understanding is that the delivered perf should fail into the range between lowest_perf and highest_perf. Is that assumption correct? This happens on 5.4-based kernel, so I am in process running your series on that system to see if there is any differences. In any case, if it is a bug it is pre-existing, but I'd like to understand a bit better in that front first.