Re: [RFC 5/9] sched: cpufreq: remove smp_processor_id() in remote paths

From: Rafael J. Wysocki
Date: Wed Mar 29 2017 - 17:38:14 EST


On Thursday, March 09, 2017 05:15:15 PM Viresh Kumar wrote:
> From: Steve Muckle <smuckle.linux@xxxxxxxxx>
>
> Upcoming support for remote callbacks from the scheduler into schedutil
> requires that the CPU identified in the hook structure be used to
> indicate the CPU being operated on, rather than relying on
> smp_processor_id().
>
> Note that policy->cpu is passed to trace_cpu_frequency() in fast switch
> path, as it is safe to use any CPU which is managed by the current
> policy.

This should be commented about in the code too IMO.

>
> Signed-off-by: Steve Muckle <smuckle.linux@xxxxxxxxx>
> [ vk: updated commit log, minor code cleanups and use policy->cpu for
> traces ]
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> kernel/sched/cpufreq_schedutil.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index a418544c51b1..b168c31f1c8f 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -96,7 +96,7 @@ static void sugov_fast_switch(struct cpufreq_policy *policy,
> return;
>
> policy->cur = next_freq;
> - trace_cpu_frequency(next_freq, smp_processor_id());
> + trace_cpu_frequency(next_freq, policy->cpu);
> }
>
> static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> @@ -106,7 +106,7 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
>
> if (policy->fast_switch_enabled) {
> if (sg_policy->next_freq == next_freq) {
> - trace_cpu_frequency(policy->cur, smp_processor_id());
> + trace_cpu_frequency(policy->cur, policy->cpu);
> return;
> }
> sg_policy->next_freq = next_freq;
> @@ -157,12 +157,12 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> return cpufreq_driver_resolve_freq(policy, freq);
> }
>
> -static void sugov_get_util(unsigned long *util, unsigned long *max)
> +static void sugov_get_util(unsigned long *util, unsigned long *max, int cpu)
> {
> - struct rq *rq = this_rq();
> + struct rq *rq = cpu_rq(cpu);
> unsigned long cfs_max;
>
> - cfs_max = arch_scale_cpu_capacity(NULL, smp_processor_id());
> + cfs_max = arch_scale_cpu_capacity(NULL, cpu);
>
> *util = min(rq->cfs.avg.util_avg, cfs_max);
> *max = cfs_max;
> @@ -216,7 +216,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
> if (flags & SCHED_CPUFREQ_RT_DL) {
> next_f = policy->cpuinfo.max_freq;
> } else {
> - sugov_get_util(&util, &max);
> + sugov_get_util(&util, &max, hook->cpu);

Why is this not racy?

> sugov_iowait_boost(sg_cpu, &util, &max);
> next_f = get_next_freq(sg_policy, util, max);
> }
> @@ -272,7 +272,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> unsigned long util, max;
> unsigned int next_f;
>
> - sugov_get_util(&util, &max);
> + sugov_get_util(&util, &max, hook->cpu);
>

And here?

> raw_spin_lock(&sg_policy->update_lock);
>
>

Thanks,
Rafael