Re: [PATCH 2/5] cpufreq: schedutil: support scheduler cpufreq callbacks on remote CPUs

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, May 9, 2016 at 11:20 PM, Steve Muckle <steve.muckle@linaro.org> wrote:
> In preparation for the scheduler cpufreq callback happening on remote
> CPUs, add support for this in schedutil.
>
> Schedutil currently requires the callback occur on the CPU being
> updated in order to support fast frequency switches. Remove this
> limitation by checking for the current CPU being outside the target
> CPU's cpufreq policy and if this is the case, enqueuing an irq_work on
> the target CPU. The irq_work for schedutil is modified to carry out a
> fast frequency switch if that is enabled for the policy.
>
> If the callback occurs on a CPU within the target CPU's policy, the
> transition is carried out on the local CPU.
>
> Signed-off-by: Steve Muckle <smuckle@linaro.org>
> ---
>  kernel/sched/cpufreq_schedutil.c | 86 ++++++++++++++++++++++++++++++----------
>  1 file changed, 65 insertions(+), 21 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 154ae3a51e86..c81f9432f520 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -76,27 +76,61 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
>         return delta_ns >= sg_policy->freq_update_delay_ns;
>  }
>
> -static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> +static void sugov_fast_switch(struct sugov_policy *sg_policy, int cpu,
> +                             unsigned int next_freq)
> +{
> +       struct cpufreq_policy *policy = sg_policy->policy;
> +
> +       next_freq = cpufreq_driver_fast_switch(policy, next_freq);
> +       if (next_freq == CPUFREQ_ENTRY_INVALID)
> +               return;
> +
> +       policy->cur = next_freq;
> +       trace_cpu_frequency(next_freq, cpu);
> +}
> +
> +#ifdef CONFIG_SMP

schedutil depends on CONFIG_SMP now, so that's not necessary at least
for the time being.

> +static inline bool sugov_queue_remote_callback(struct sugov_policy *sg_policy,
> +                                        int cpu)
> +{
> +       struct cpufreq_policy *policy = sg_policy->policy;
> +
> +       if (!cpumask_test_cpu(smp_processor_id(), policy->cpus)) {

This check is overkill for policies that aren't shared (and we have a
special case for them already).

> +               sg_policy->work_in_progress = true;
> +               irq_work_queue_on(&sg_policy->irq_work, cpu);
> +               return true;
> +       }
> +
> +       return false;
> +}
> +#else
> +static inline bool sugov_queue_remote_callback(struct sugov_policy *sg_policy,
> +                                        int cpu)
> +{
> +       return false;
> +}
> +#endif
> +
> +static void sugov_update_commit(struct sugov_cpu *sg_cpu, int cpu, u64 time,

It looks like you might pass hook here instead of the sg_cpu, cpu pair.

>                                 unsigned int next_freq)
>  {
> +       struct sugov_policy *sg_policy = sg_cpu->sg_policy;
>         struct cpufreq_policy *policy = sg_policy->policy;
>
>         sg_policy->last_freq_update_time = time;
>
> +       if (sg_policy->next_freq == next_freq) {
> +               trace_cpu_frequency(policy->cur, cpu);
> +               return;
> +       }

There was a reason why I put the above under the fast_switch_enabled
branch and it was because this check/trace is not necessary otherwise.

> +       sg_policy->next_freq = next_freq;
> +
> +       if (sugov_queue_remote_callback(sg_policy, cpu))
> +               return;
> +
>         if (policy->fast_switch_enabled) {
> -               if (sg_policy->next_freq == next_freq) {
> -                       trace_cpu_frequency(policy->cur, smp_processor_id());
> -                       return;
> -               }
> -               sg_policy->next_freq = next_freq;
> -               next_freq = cpufreq_driver_fast_switch(policy, next_freq);
> -               if (next_freq == CPUFREQ_ENTRY_INVALID)
> -                       return;
> -
> -               policy->cur = next_freq;
> -               trace_cpu_frequency(next_freq, smp_processor_id());
> -       } else if (sg_policy->next_freq != next_freq) {
> -               sg_policy->next_freq = next_freq;
> +               sugov_fast_switch(sg_policy, cpu, next_freq);
> +       } else {
>                 sg_policy->work_in_progress = true;
>                 irq_work_queue(&sg_policy->irq_work);
>         }
> @@ -142,12 +176,13 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
>
>         next_f = util == ULONG_MAX ? policy->cpuinfo.max_freq :
>                         get_next_freq(policy, util, max);
> -       sugov_update_commit(sg_policy, time, next_f);
> +       sugov_update_commit(sg_cpu, hook->cpu, time, next_f);
>  }
>
> -static unsigned int sugov_next_freq_shared(struct sugov_policy *sg_policy,
> +static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu,
>                                            unsigned long util, unsigned long max)
>  {
> +       struct sugov_policy *sg_policy = sg_cpu->sg_policy;
>         struct cpufreq_policy *policy = sg_policy->policy;
>         unsigned int max_f = policy->cpuinfo.max_freq;
>         u64 last_freq_update_time = sg_policy->last_freq_update_time;
> @@ -161,10 +196,10 @@ static unsigned int sugov_next_freq_shared(struct sugov_policy *sg_policy,
>                 unsigned long j_util, j_max;
>                 s64 delta_ns;
>
> -               if (j == smp_processor_id())
> +               j_sg_cpu = &per_cpu(sugov_cpu, j);
> +               if (j_sg_cpu == sg_cpu)
>                         continue;
>
> -               j_sg_cpu = &per_cpu(sugov_cpu, j);
>                 /*
>                  * If the CPU utilization was last updated before the previous
>                  * frequency update and the time elapsed between the last update
> @@ -204,8 +239,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>         sg_cpu->last_update = time;
>
>         if (sugov_should_update_freq(sg_policy, time)) {
> -               next_f = sugov_next_freq_shared(sg_policy, util, max);
> -               sugov_update_commit(sg_policy, time, next_f);
> +               next_f = sugov_next_freq_shared(sg_cpu, util, max);
> +               sugov_update_commit(sg_cpu, hook->cpu, time, next_f);
>         }
>
>         raw_spin_unlock(&sg_policy->update_lock);
> @@ -226,9 +261,18 @@ static void sugov_work(struct work_struct *work)
>  static void sugov_irq_work(struct irq_work *irq_work)
>  {
>         struct sugov_policy *sg_policy;
> +       struct cpufreq_policy *policy;
>
>         sg_policy = container_of(irq_work, struct sugov_policy, irq_work);
> -       schedule_work_on(smp_processor_id(), &sg_policy->work);
> +       policy = sg_policy->policy;
> +
> +       if (policy->fast_switch_enabled) {
> +               sugov_fast_switch(sg_policy, smp_processor_id(),
> +                                 sg_policy->next_freq);
> +               sg_policy->work_in_progress = false;
> +       } else {
> +               schedule_work_on(smp_processor_id(), &sg_policy->work);
> +       }
>  }
>
>  /************************** sysfs interface ************************/
> --
> 2.4.10
>