cpufreq: intel_pstate: Set P-state upfront in performance mode

After commit a4675fbc (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: a4675fbc (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

@@ -1142,10 +1142,8 @@ static void intel_pstate_get_min_max(struct cpudata *cpu, int *min, int *max)
 	*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;
 	/*
@@ -1157,6 +1155,20 @@ static void intel_pstate_set_min_pstate(struct cpudata *cpu)
 		      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();
@@ -1491,7 +1503,7 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
 	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) {
@@ -1535,6 +1547,15 @@ static int intel_pstate_set_policy(struct cpufreq_policy *policy)
 	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);