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SubjectRe: [RFC][PATCH 3/4] cpuidle: Allow cpuidle drivers to take over RCU-idle
On Tue, 15 Sep 2020 at 12:44, Peter Zijlstra <peterz@infradead.org> 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@infradead.org>

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

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;
>
>

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