RE: [RFC/RFT][PATCH v2] cpufreq: intel_pstate: Proportional algorithm for Atom
From: Doug Smythies
Date: Wed Oct 05 2016 - 19:59:44 EST
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 "?" ?
I can not get this patch to compile,
but if I change that ":" to a "?" (as in the previous version of this patch)
> + cpu->pstate.max_pstate : cpu->pstate.turbo_pstate;
> + target += target >> 2;
> + target = mul_fp(target, busy_frac);
> + if (target < cpu->pstate.min_pstate)
> + target = cpu->pstate.min_pstate;
> + /*
> + * If the average P-state during the previous cycle was higher than the
> + * current target, add 50% of the difference to the target to reduce
> + * possible performance oscillations and offset possible performance
> + * loss related to moving the workload from one CPU to another within
> + * a package/module.
> + */
> + avg_pstate = get_avg_pstate(cpu);
> + if (avg_pstate > target)
> + target += (avg_pstate - target) >> 1;
> + return target;
> static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)