Re: [RFC][PATCH 3/4] cpuidle: Allow cpuidle drivers to take over RCU-idle

[Ulf Hansson]

On Tue, 15 Sep 2020 at 12:44, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> Some drivers have to do significant work, some of which relies on RCU
> still being active. Instead of using RCU_NONIDLE in the drivers and
> flipping RCU back on, allow drivers to take over RCU-idle duty.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Reviewed-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>

Kind regards
Uffe

> ---
>  drivers/cpuidle/cpuidle.c |   15 ++++++++++-----
>  include/linux/cpuidle.h   |    1 +
>  2 files changed, 11 insertions(+), 5 deletions(-)
>
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -138,6 +138,7 @@ static void enter_s2idle_proper(struct c
>                                 struct cpuidle_device *dev, int index)
>  {
>         ktime_t time_start, time_end;
> +       struct cpuidle_state *target_state = &drv->states[index];
>
>         time_start = ns_to_ktime(local_clock());
>
> @@ -153,8 +154,9 @@ static void enter_s2idle_proper(struct c
>          * suspended is generally unsafe.
>          */
>         stop_critical_timings();
> -       rcu_idle_enter();
> -       drv->states[index].enter_s2idle(dev, drv, index);
> +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> +               rcu_idle_enter();
> +       target_state->enter_s2idle(dev, drv, index);
>         if (WARN_ON_ONCE(!irqs_disabled()))
>                 local_irq_disable();
>         /*
> @@ -162,7 +164,8 @@ static void enter_s2idle_proper(struct c
>          * first CPU executing it calls functions containing RCU read-side
>          * critical sections, so tell RCU about that.
>          */
> -       rcu_idle_exit();
> +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> +               rcu_idle_exit();
>         tick_unfreeze();
>         start_critical_timings();
>
> @@ -239,9 +242,11 @@ int cpuidle_enter_state(struct cpuidle_d
>         time_start = ns_to_ktime(local_clock());
>
>         stop_critical_timings();
> -       rcu_idle_enter();
> +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> +               rcu_idle_enter();
>         entered_state = target_state->enter(dev, drv, index);
> -       rcu_idle_exit();
> +       if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
> +               rcu_idle_exit();
>         start_critical_timings();
>
>         sched_clock_idle_wakeup_event();
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -82,6 +82,7 @@ struct cpuidle_state {
>  #define CPUIDLE_FLAG_UNUSABLE          BIT(3) /* avoid using this state */
>  #define CPUIDLE_FLAG_OFF               BIT(4) /* disable this state by default */
>  #define CPUIDLE_FLAG_TLB_FLUSHED       BIT(5) /* idle-state flushes TLBs */
> +#define CPUIDLE_FLAG_RCU_IDLE          BIT(6) /* idle-state takes care of RCU */
>
>  struct cpuidle_device_kobj;
>  struct cpuidle_state_kobj;
>
>