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