Re: [RFC/RFT][PATCH v2] cpufreq: intel_pstate: Proportional algorithm for Atom
From: Rafael J. Wysocki
Date: Thu Oct 06 2016 - 07:58:11 EST
On Thu, Oct 6, 2016 at 1:58 AM, Doug Smythies <dsmythies@xxxxxxxxx> wrote:
> Hi Rafael,
> It doesn't compile for me. See further down.
> On 2016.10.05 06:15 Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> The PID algorithm used by the intel_pstate driver tends to drive
>> performance to the minimum for workloads with utilization below the
>> setpoint, which is undesirable, so replace it with a modified
>> "proportional" algorithm on Atom.
>> The new algorithm will set the new P-state to be 1.25 times the
>> available maximum times the (frequency-invariant) utilization during
>> the previous sampling period except when the target P-state computed
>> this way is lower than the average P-state during the previous
>> sampling period. In the latter case, it will increase the target by
>> 50% of the difference between it and the average P-state to prevent
>> performance from dropping down too fast in some cases.
>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> It is better to compare the average P-state to the target (than to
>> compare the average perf ratio to the utilization), because that takes
>> turbo into account more accurately.
>> Plus if the target is below the min, it is better to compare the min
>> to the average instead of comparing the target to it.
>> drivers/cpufreq/intel_pstate.c | 22 +++++++++++++++++++++-
>> 1 file changed, 21 insertions(+), 1 deletion(-)
>> Index: linux-pm/drivers/cpufreq/intel_pstate.c
>> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
>> +++ linux-pm/drivers/cpufreq/intel_pstate.c
>> @@ -1232,6 +1232,7 @@ static inline int32_t get_target_pstate_
>> struct sample *sample = &cpu->sample;
>> int32_t busy_frac, boost;
>> + int target, avg_pstate;
>> busy_frac = div_fp(sample->mperf, sample->tsc);
>> @@ -1242,7 +1243,26 @@ static inline int32_t get_target_pstate_
>> busy_frac = boost;
>> sample->busy_scaled = busy_frac * 100;
>> - return get_avg_pstate(cpu) - pid_calc(&cpu->pid, sample->busy_scaled);
>> + target = limits->no_turbo || limits->turbo_disabled :
> For proper conditional expression syntax, shouldn't that be a "?" ?
Yes, my bad, sorry.
I'll send a v3 shortly.