[PATCH 3/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks

Patrick Bellasi
2017-03-02T15:49:12Z

The policy in use for RT/DL tasks sets the maximum frequency when a task
in these classes calls for a cpufreq_update_this_cpu(). However, the
current implementation might cause a frequency drop while a RT/DL task
is still running, just because for example a FAIR task wakes up and is
enqueued in the same CPU.

This issue is due to the sg_cpu's flags being overwritten at each call
of sugov_update_*. The wakeup of a FAIR task resets the flags and can
trigger a frequency update thus affecting the currently running RT/DL
task.

This can be fixed, in shared frequency domains, by adding (instead of
overwriting) the new flags before triggering a frequency update. This
grants to stay at least at the frequency requested by the RT/DL class,
which is the maximum one for the time being, but can also be lower when
for example DL will be extended to provide a precise bandwidth
requirement.

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 | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index a3fe5e4..b98a167 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -196,10 +196,21 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
unsigned int flags)
{
struct sugov_cpu *sg_cpu = container_of(hook, struct sugov_cpu, update_util);
+ struct task_struct *curr = cpu_curr(smp_processor_id());
struct sugov_policy *sg_policy = sg_cpu->sg_policy;
struct cpufreq_policy *policy = sg_policy->policy;
unsigned long util, max;
unsigned int next_f;
+ bool rt_mode;
+
+ /*
+ * While RT/DL tasks are running we do not want FAIR tasks to
+ * overvrite this CPU's flags, still we can update utilization and
+ * frequency (if required/possible) to be fair with these tasks.
+ */
+ rt_mode = task_has_dl_policy(curr) ||
+ task_has_rt_policy(curr) ||
+ (flags & SCHED_CPUFREQ_RT_DL);

sugov_set_iowait_boost(sg_cpu, time, flags);
sg_cpu->last_update = time;
@@ -207,7 +218,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
if (!sugov_should_update_freq(sg_policy, time))
return;

- if (flags & SCHED_CPUFREQ_RT_DL) {
+ if (rt_mode) {
next_f = policy->cpuinfo.max_freq;
} else {
sugov_get_util(&util, &max);
@@ -278,6 +289,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
struct task_struct *curr = cpu_curr(cpu);
unsigned long util, max;
unsigned int next_f;
+ bool rt_mode;

sugov_get_util(&util, &max);

@@ -293,15 +305,29 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
if (curr == sg_policy->thread)
goto done;

+ /*
+ * While RT/DL tasks are running we do not want FAIR tasks to
+ * overwrite this CPU's flags, still we can update utilization and
+ * frequency (if required/possible) to be fair with these tasks.
+ */
+ rt_mode = task_has_dl_policy(curr) ||
+ task_has_rt_policy(curr) ||
+ (flags & SCHED_CPUFREQ_RT_DL);
+ if (rt_mode)
+ sg_cpu->flags |= flags;
+ else
+ sg_cpu->flags = flags;
+
sg_cpu->util = util;
sg_cpu->max = max;
- sg_cpu->flags = flags;

sugov_set_iowait_boost(sg_cpu, time, flags);
sg_cpu->last_update = time;

if (sugov_should_update_freq(sg_policy, time)) {
- next_f = sugov_next_freq_shared(sg_cpu, util, max, flags);
+ next_f = sg_policy->policy->cpuinfo.max_freq;
+ if (!rt_mode)
+ next_f = sugov_next_freq_shared(sg_cpu, util, max, flags);
sugov_update_commit(sg_policy, time, next_f);
}

--
2.7.4