Re: [RFCv5 PATCH 39/46] sched/cpufreq_sched: use static key for cpu frequency selection

Michael Turquette
2015-07-08T15:20:23Z

Quoting Morten Rasmussen (2015-07-07 11:24:22)
> From: Juri Lelli <juri.lelli@arm.com>
>
> Introduce a static key to only affect scheduler hot paths when sched
> governor is enabled.
>
> cc: Ingo Molnar <mingo@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
>
> Signed-off-by: Juri Lelli <juri.lelli@arm.com>
> ---
> kernel/sched/cpufreq_sched.c | 14 ++++++++++++++
> kernel/sched/fair.c | 1 +
> kernel/sched/sched.h | 6 ++++++
> 3 files changed, 21 insertions(+)
>
> diff --git a/kernel/sched/cpufreq_sched.c b/kernel/sched/cpufreq_sched.c
> index 5020f24..2968f3a 100644
> --- a/kernel/sched/cpufreq_sched.c
> +++ b/kernel/sched/cpufreq_sched.c
> @@ -203,6 +203,18 @@ void cpufreq_sched_set_cap(int cpu, unsigned long capacity)
> return;
> }
>
> +static inline void set_sched_energy_freq(void)
> +{
> + if (!sched_energy_freq())
> + static_key_slow_inc(&__sched_energy_freq);
> +}
> +
> +static inline void clear_sched_energy_freq(void)
> +{
> + if (sched_energy_freq())
> + static_key_slow_dec(&__sched_energy_freq);
> +}
> +
> static int cpufreq_sched_start(struct cpufreq_policy *policy)
> {
> struct gov_data *gd;
> @@ -243,6 +255,7 @@ static int cpufreq_sched_start(struct cpufreq_policy *policy)
>
> policy->governor_data = gd;
> gd->policy = policy;
> + set_sched_energy_freq();
> return 0;
>
> err:
> @@ -254,6 +267,7 @@ static int cpufreq_sched_stop(struct cpufreq_policy *policy)
> {
> struct gov_data *gd = policy->governor_data;
>
> + clear_sched_energy_freq();

<paranoia>

These controls are exposed to userspace via cpufreq sysfs knobs. Should
we use a struct static_key_deferred and static_key_slow_dec_deferred()
instead? This helps avoid a possible attack vector for slowing down the
system.

</paranoia>

I don't really know what a sane default rate limit would be in that case
though. Otherwise feel free to add:

Reviewed-by: Michael Turquette <mturquette@baylibre.com>

Regards,
Mike

> if (cpufreq_driver_might_sleep()) {
> kthread_stop(gd->task);
> }
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f7cb6c9..d395bc9 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4282,6 +4282,7 @@ static inline void hrtick_update(struct rq *rq)
> #endif
>
> static bool cpu_overutilized(int cpu);
> +struct static_key __sched_energy_freq __read_mostly = STATIC_KEY_INIT_FALSE;
>
> /*
> * The enqueue_task method is called before nr_running is
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 30aa0c4..b5e27d9 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1476,6 +1476,12 @@ unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
> }
> #endif
>
> +extern struct static_key __sched_energy_freq;
> +static inline bool sched_energy_freq(void)
> +{
> + return static_key_false(&__sched_energy_freq);
> +}
> +
> #ifdef CONFIG_CPU_FREQ_GOV_SCHED
> void cpufreq_sched_set_cap(int cpu, unsigned long util);
> #else
> --
> 1.9.1
>
> --
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