On 08/27/2013 07:07 PM, Viresh Kumar wrote:
On 27 August 2013 21:16, Stratos Karafotis <stratosk@xxxxxxxxxxxx> 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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