[PATCH 2/6] cpufreq: schedutil: ignore the sugov kthread for frequencies selections

Patrick Bellasi
2017-03-02T15:49:15Z

In system where multiple CPUs shares the same frequency domain a small
workload on a CPU can still be subject frequency spikes, generated by
the activation of the sugov's kthread.

Since the sugov kthread is a special RT task, which goal is just that to
activate a frequency transition, it does not make sense for it to bias
the schedutil's frequency selection.

This patch exploits the information related to the current task to silently
ignore cpufreq_update_this_cpu() calls, coming from the RT scheduler, while
the sugov kthread is running.

Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
---
kernel/sched/cpufreq_schedutil.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 084a98b..a3fe5e4 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -274,6 +274,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
{
struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
struct sugov_policy *sg_policy = sg_cpu->sg_policy;
+ unsigned int cpu = smp_processor_id();
+ struct task_struct *curr = cpu_curr(cpu);
unsigned long util, max;
unsigned int next_f;

@@ -287,6 +289,10 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
goto done;
}

+ /* Skip updates generated by sugov kthreads */
+ if (curr == sg_policy->thread)
+ goto done;
+
sg_cpu->util = util;
sg_cpu->max = max;
sg_cpu->flags = flags;
--
2.7.4