linux-kernel - [PATCH] cpufreq: intel_pstate: Always set max P-state in performance mode

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Message-ID: <1490845.P5jEmYeGuo@vostro.rjw.lan>
Date:   Mon, 24 Oct 2016 15:20:39 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Linux PM list <linux-pm@...r.kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] cpufreq: intel_pstate: Always set max P-state in performance mode

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

The only times when intel_pstate checks the policy set for a given
CPU is the initialization of that CPU and updates of its settings
from cpufreq leading to intel_pstate_set_policy() invocatios.

That is insufficient, however, because intel_pstate uses the same
P-state selection function for all CPUs regardless of the policy
setting for each of them and the P-state limits are shared between
them.  Thus if the policy is set to "performance" for a particular
CPU, it may not behave as expected if the cpufreq settings are
changed subsequently for another CPU.

That can be easily demonstrated by writing "performance" to
scaling_governor for all CPUs and then switching it to "powersave"
for one of them in which case all of the CPUs will behave as though
their scaling_governor were "powersave" (even though the policy
still appears to be "performance" for the remaining CPUs).

Fix this problem by modifying intel_pstate_adjust_busy_pstate() to
always set the P-state to the maximum allowed by the current limits
if the policy is set to "performance" for the given CPU.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/intel_pstate.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -179,6 +179,7 @@ struct _pid {
 /**
  * struct cpudata -	Per CPU instance data storage
  * @cpu:		CPU number for this instance data
+ * @policy:		CPUFreq policy value
  * @update_util:	CPUFreq utility callback information
  * @update_util_set:	CPUFreq utility callback is set
  * @iowait_boost:	iowait-related boost fraction
@@ -201,6 +202,7 @@ struct _pid {
 struct cpudata {
 	int cpu;
 
+	unsigned int policy;
 	struct update_util_data update_util;
 	bool   update_util_set;
 
@@ -1331,7 +1333,8 @@ static inline void intel_pstate_adjust_b
 
 	from = cpu->pstate.current_pstate;
 
-	target_pstate = pstate_funcs.get_target_pstate(cpu);
+	target_pstate = cpu->policy == CPUFREQ_POLICY_PERFORMANCE ?
+		cpu->pstate.turbo_pstate : pstate_funcs.get_target_pstate(cpu);
 
 	intel_pstate_update_pstate(cpu, target_pstate);
 
@@ -1498,6 +1501,8 @@ static int intel_pstate_set_policy(struc
 		 policy->cpuinfo.max_freq, policy->max);
 
 	cpu = all_cpu_data[policy->cpu];
+	cpu->policy = policy->policy;
+
 	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) {
@@ -1505,7 +1510,7 @@ static int intel_pstate_set_policy(struc
 		policy->max = policy->cpuinfo.max_freq;
 	}
 
-	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
+	if (cpu->policy == CPUFREQ_POLICY_PERFORMANCE) {
 		limits = &performance_limits;
 		if (policy->max >= policy->cpuinfo.max_freq) {
 			pr_debug("set performance\n");
@@ -1541,7 +1546,7 @@ static int intel_pstate_set_policy(struc
 	limits->max_perf = round_up(limits->max_perf, FRAC_BITS);
 
  out:
-	if (policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
+	if (cpu->policy == CPUFREQ_POLICY_PERFORMANCE) {
 		/*
 		 * NOHZ_FULL CPUs need this as the governor callback may not
 		 * be invoked on them.