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Subject[PATCH v2] cpufreq: intel_pstate: Avoid unnecessary synchronize_sched() during initialization
Date
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 <yex.tian@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
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, &cpu->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
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