[PATCH v2] cpufreq: intel_pstate: Avoid unnecessary synchronize_sched() during initialization

[Chen Yu]

Currently in intel_pstate_clear_update_util_hook, after
clearing the utilization update hook, we leverage
synchronize_sched() to deal with synchronization, which
is a little bit time-costly because synchronize_sched()
has to wait for all the CPUs to go through a grace period.

Actually, the synchronize_sched() is not necessary if the utilization
update hook has not been set for the given CPU yet, so make the driver
check if that's the case and avoid the synchronize_sched() call in
that case.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=116371
Tested-by: Tian Ye 
Signed-off-by: Chen Yu 
---
v2:
 - Rewrite the commit log according to Rafael's suggestion.
---
 drivers/cpufreq/intel_pstate.c | 9 +
 1 file changed, 9 insertions(+)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index b230eba..9811e4e 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -162,6 +162,7 @@ struct _pid {
  * struct cpudata -Per CPU instance data storage
  * @cpu:   CPU number for this instance data
  * @update_util:   CPUFreq utility callback information
+ * @update_util_set:   CPUFreq utility callback is set
  * @pstate:Stores P state limits for this CPU
  * @vid:   Stores VID limits for this CPU
  * @pid:   Stores PID parameters for this CPU
@@ -179,6 +180,7 @@ struct cpudata {
int cpu;
 
struct update_util_data update_util;
+   bool   update_util_set;
 
struct pstate_data pstate;
struct vid_data vid;
@@ -1287,11 +1289,18 @@ static void intel_pstate_set_update_util_hook(unsigned 
int cpu_num)
/* Prevent intel_pstate_update_util() from using stale data. */
cpu->sample.time = 0;
cpufreq_set_update_util_data(cpu_num, >update_util);
+   cpu->update_util_set = true;
 }
 
 static void intel_pstate_clear_update_util_hook(unsigned int cpu)
 {
+   struct cpudata *cpu_data = all_cpu_data[cpu];
+
+   if (!cpu_data->update_util_set)
+   return;
+
cpufreq_set_update_util_data(cpu, NULL);
+   cpu_data->update_util_set = false;
synchronize_sched();
 }
 
-- 
2.7.4

[PATCH v2] cpufreq: intel_pstate: Avoid unnecessary synchronize_sched() during initialization

[Chen Yu]

Currently in intel_pstate_clear_update_util_hook, after
clearing the utilization update hook, we leverage
synchronize_sched() to deal with synchronization, which
is a little bit time-costly because synchronize_sched()
has to wait for all the CPUs to go through a grace period.

Actually, the synchronize_sched() is not necessary if the utilization
update hook has not been set for the given CPU yet, so make the driver
check if that's the case and avoid the synchronize_sched() call in
that case.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=116371
Tested-by: Tian Ye 
Signed-off-by: Chen Yu 
---
v2:
 - Rewrite the commit log according to Rafael's suggestion.
---
 drivers/cpufreq/intel_pstate.c | 9 +
 1 file changed, 9 insertions(+)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index b230eba..9811e4e 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -162,6 +162,7 @@ struct _pid {
  * struct cpudata -Per CPU instance data storage
  * @cpu:   CPU number for this instance data
  * @update_util:   CPUFreq utility callback information
+ * @update_util_set:   CPUFreq utility callback is set
  * @pstate:Stores P state limits for this CPU
  * @vid:   Stores VID limits for this CPU
  * @pid:   Stores PID parameters for this CPU
@@ -179,6 +180,7 @@ struct cpudata {
int cpu;
 
struct update_util_data update_util;
+   bool   update_util_set;
 
struct pstate_data pstate;
struct vid_data vid;
@@ -1287,11 +1289,18 @@ static void intel_pstate_set_update_util_hook(unsigned 
int cpu_num)
/* Prevent intel_pstate_update_util() from using stale data. */
cpu->sample.time = 0;
cpufreq_set_update_util_data(cpu_num, >update_util);
+   cpu->update_util_set = true;
 }
 
 static void intel_pstate_clear_update_util_hook(unsigned int cpu)
 {
+   struct cpudata *cpu_data = all_cpu_data[cpu];
+
+   if (!cpu_data->update_util_set)
+   return;
+
cpufreq_set_update_util_data(cpu, NULL);
+   cpu_data->update_util_set = false;
synchronize_sched();
 }
 
-- 
2.7.4