intel_pstate: Avoid unnecessary synchronize_sched() during initialization

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 then.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=116371
Tested-by: Tian Ye <yex.tian@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
[ rjw : Rebase ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index cde1a4ecaa6ea03b8358fe26c54071481a485a89..36953b5f18de9b5477961c71895318553518b73a 100644 (file)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -168,6 +168,7 @@ 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
@@ -187,6 +188,7 @@ struct cpudata {
        int cpu;
 
        struct update_util_data update_util;
+       bool   update_util_set;
 
        struct pstate_data pstate;
        struct vid_data vid;
@@ -1417,11 +1419,18 @@ static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
        cpu->sample.time = 0;
        cpufreq_add_update_util_hook(cpu_num, &cpu->update_util,
                                     intel_pstate_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_remove_update_util_hook(cpu);
+       cpu_data->update_util_set = false;
        synchronize_sched();
 }