Re: [PATCH] cpufreq: intel_pstate: Set P-state upfront in performance mode

Srinivas Pandruvada
2016-10-21T15:11:44Z

On Wed, 2016-10-19 at 02:57 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> After commit a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with
> utilization update callbacks) the cpufreq governor callbacks may not
> be invoked on NOHZ_FULL CPUs and, in particular, switching to the
> "performance" policy via sysfs may not have any effect on them.  That
> is a problem, because it usually is desirable to squeeze the last
> bit of performance out of those CPUs, so work around it by setting
> the maximum P-state (within the limits) in intel_pstate_set_policy()
> upfront when the policy is CPUFREQ_POLICY_PERFORMANCE.
>
> Fixes: a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with
> utilization update callbacks)
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

> ---
>  drivers/cpufreq/intel_pstate.c |   29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
>
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -1137,10 +1137,8 @@ static void intel_pstate_get_min_max(str
>   *min = clamp_t(int, min_perf, cpu->pstate.min_pstate,
> max_perf);
>  }
>
> -static void intel_pstate_set_min_pstate(struct cpudata *cpu)
> +static void intel_pstate_set_pstate(struct cpudata *cpu, int pstate)
>  {
> - int pstate = cpu->pstate.min_pstate;
> -
>   trace_cpu_frequency(pstate * cpu->pstate.scaling, cpu->cpu);
>   cpu->pstate.current_pstate = pstate;
>   /*
> @@ -1152,6 +1150,20 @@ static void intel_pstate_set_min_pstate(
>         pstate_funcs.get_val(cpu, pstate));
>  }
>
> +static void intel_pstate_set_min_pstate(struct cpudata *cpu)
> +{
> + intel_pstate_set_pstate(cpu, cpu->pstate.min_pstate);
> +}
> +
> +static void intel_pstate_max_within_limits(struct cpudata *cpu)
> +{
> + int min_pstate, max_pstate;
> +
> + update_turbo_state();
> + intel_pstate_get_min_max(cpu, &min_pstate, &max_pstate);
> + intel_pstate_set_pstate(cpu, max_pstate);
> +}
> +
>  static void intel_pstate_get_cpu_pstates(struct cpudata *cpu)
>  {
>   cpu->pstate.min_pstate = pstate_funcs.get_min();
> @@ -1485,7 +1497,7 @@ static int intel_pstate_set_policy(struc
>   pr_debug("set_policy cpuinfo.max %u policy->max %u\n",
>    policy->cpuinfo.max_freq, policy->max);
>
> - cpu = all_cpu_data[0];
> + cpu = all_cpu_data[policy->cpu];
>   if (cpu->pstate.max_pstate_physical > cpu->pstate.max_pstate
> &&
>       policy->max < policy->cpuinfo.max_freq &&
>       policy->max > cpu->pstate.max_pstate * cpu-
> >pstate.scaling) {
> @@ -1529,6 +1541,15 @@ static int intel_pstate_set_policy(struc
>   limits->max_perf = round_up(limits->max_perf, FRAC_BITS);
>
>   out:
> + if (policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
> + /*
> +  * NOHZ_FULL CPUs need this as the governor callback
> may not
> +  * be invoked on them.
> +  */
> + intel_pstate_clear_update_util_hook(policy->cpu);
> + intel_pstate_max_within_limits(cpu);
> + }
> +
>   intel_pstate_set_update_util_hook(policy->cpu);
>
>   intel_pstate_hwp_set_policy(policy);
>