Messages in this thread | | | Date | Tue, 27 Aug 2013 20:34:15 +0300 | From | Stratos Karafotis <> | Subject | Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range |
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On 08/27/2013 07:07 PM, Viresh Kumar wrote: > On 27 August 2013 21:16, Stratos Karafotis <stratosk@semaphore.gr> wrote: >> I think we should keep these checks because: >> >> 1) They shorten the execution code (there is no unnecessary call of >> __cpufreq_driver_target) > > I don't really count this one.. This is how code is present everywhere in > kernel.. These checks are present in routines and callers don't need to > take care of them..
I mean that if we will get rid of the code you mentioned, we will have an extra call to function __cpufreq_driver_target in some cases.
>> 2) In case my patch will be accepted, we need them to avoid continuously >> increase of dbs_info->requested_freq.With my patch the requested_freq >> can temporarily overcome policy->min and policy->max. __cpufreq_driver_target >> will select the correct frequency (within policy->min and policy->max). >> Then, dbs_cpufreq_notifier will adjust requested_freq. > > Sorry, I couldn't understand what you meant here :( >
I'm sorry. Let me try to explain this better.
With my patch, dbs_info->requested_freq will not be capped within policy->min and policy->max in cs_check_cpu. So, temporarily it may have a value greater than policy->max or lower that policy->min. When we call __cpufreq_driver_target, the correct frequency will be selected because __cpufreq_driver_target takes care to adjust the target frequency within policy range. But, eventually, dbs_cpufreq_notifier will adjust dbs_info->requested within policy range, if needed.
If we remove if (dbs_info->requested_freq == policy->max) return; and if (policy->cur == policy->min) return;
request_freq will keep increasing or decreasing in each iteration and finally will overflow or underflow.
Consider, for example, that in a CPU with policy->max = 1000MHz the current frequency is 950MHz. With a constant load above up_threshold, the requested_freq in first iteration will be 1000MHz and __cpufreq_driver_target will select 1000MHz freq.
In second iteration, requested_freq will be 1050MHz, and __cpufreq_driver_target will select 1000MHz. dbs_cpufreq_notifier will adjust requested_freq back to 1000MHz.
In next iterations, dbs_cpufreq_notifier will not be called, so we need the above check (dbs_info->requested_freq == policy->max) to prevent requested_freq to grow arbitrary.
I hope my explanation was better now. :)
Thanks, Stratos
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