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

From: Qian Cai
Date: Wed Jun 23 2021 - 08:57:55 EST

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.