From c072a388d59a1d48e36864d0e66f42d71745be1c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 7 Jan 2011 02:33:47 -0800 Subject: rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status Because the adaptive synchronize_srcu_expedited() approach has worked very well in testing, remove the kernel parameter and replace it by a C-preprocessor macro. If someone finds problems with this approach, a more complex and aggressively adaptive approach might be required. Longer term, SRCU will be merged with the other RCU implementations, at which point synchronize_srcu_expedited() will be event driven, just as synchronize_sched_expedited() currently is. At that point, there will be no need for this adaptive approach. Reported-by: Linus Torvalds Signed-off-by: Paul E. McKenney --- kernel/srcu.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/srcu.c b/kernel/srcu.c index 98d8c1e80ed..73ce23feaea 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -155,6 +155,16 @@ void __srcu_read_unlock(struct srcu_struct *sp, int idx) } EXPORT_SYMBOL_GPL(__srcu_read_unlock); +/* + * We use an adaptive strategy for synchronize_srcu() and especially for + * synchronize_srcu_expedited(). We spin for a fixed time period + * (defined below) to allow SRCU readers to exit their read-side critical + * sections. If there are still some readers after 10 microseconds, + * we repeatedly block for 1-millisecond time periods. This approach + * has done well in testing, so there is no need for a config parameter. + */ +#define SYNCHRONIZE_SRCU_READER_DELAY 10 + /* * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). */ @@ -207,11 +217,12 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) * will have finished executing. We initially give readers * an arbitrarily chosen 10 microseconds to get out of their * SRCU read-side critical sections, then loop waiting 1/HZ - * seconds per iteration. + * seconds per iteration. The 10-microsecond value has done + * very well in testing. */ if (srcu_readers_active_idx(sp, idx)) - udelay(CONFIG_SRCU_SYNCHRONIZE_DELAY); + udelay(SYNCHRONIZE_SRCU_READER_DELAY); while (srcu_readers_active_idx(sp, idx)) schedule_timeout_interruptible(1); -- cgit v1.2.3-70-g09d2