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Subject[PATCH v3 tip/core/rcu 20/40] srcu: Push srcu_advance_batches() fastpath into common case
Date
This commit simplifies the SRCU state machine by pushing the
srcu_advance_batches() idle-SRCU fastpath into the common case. This is
done by giving srcu_reschedule() a delay parameter, which is zero in
the call from srcu_advance_batches().

This commit is a step towards numbering callbacks in order to
efficiently handle per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcu/srcu.c | 27 +++++++--------------------
1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 7e7ecaa50dc5..821ecda873f2 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -399,8 +399,7 @@ void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
}
EXPORT_SYMBOL_GPL(call_srcu);

-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay);

/*
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
@@ -409,7 +408,6 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
{
struct rcu_synchronize rcu;
struct rcu_head *head = &rcu.head;
- bool done = false;

RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) ||
lock_is_held(&rcu_bh_lock_map) ||
@@ -431,25 +429,15 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
sp->running = true;
rcu_batch_queue(&sp->batch_check0, head);
spin_unlock_irq(&sp->queue_lock);
-
- srcu_advance_batches(sp, trycount);
- if (!rcu_batch_empty(&sp->batch_done)) {
- BUG_ON(sp->batch_done.head != head);
- rcu_batch_dequeue(&sp->batch_done);
- done = true;
- }
/* give the processing owner to work_struct */
- srcu_reschedule(sp);
+ srcu_reschedule(sp, 0);
} else {
rcu_batch_queue(&sp->batch_queue, head);
spin_unlock_irq(&sp->queue_lock);
}

- if (!done) {
- wait_for_completion(&rcu.completion);
- smp_mb(); /* Caller's later accesses after GP. */
- }
-
+ wait_for_completion(&rcu.completion);
+ smp_mb(); /* Caller's later accesses after GP. */
}

/**
@@ -639,7 +627,7 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp)
* Finished one round of SRCU grace period. Start another if there are
* more SRCU callbacks queued, otherwise put SRCU into not-running state.
*/
-static void srcu_reschedule(struct srcu_struct *sp)
+static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay)
{
bool pending = true;

@@ -653,8 +641,7 @@ static void srcu_reschedule(struct srcu_struct *sp)
}

if (pending)
- queue_delayed_work(system_power_efficient_wq,
- &sp->work, SRCU_INTERVAL);
+ queue_delayed_work(system_power_efficient_wq, &sp->work, delay);
}

/*
@@ -669,6 +656,6 @@ void process_srcu(struct work_struct *work)
srcu_collect_new(sp);
srcu_advance_batches(sp, 1);
srcu_invoke_callbacks(sp);
- srcu_reschedule(sp);
+ srcu_reschedule(sp, SRCU_INTERVAL);
}
EXPORT_SYMBOL_GPL(process_srcu);
--
2.5.2
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