From 46fdb0937f26124700fc9fc80da4776330cc00d3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 26 Oct 2010 02:11:40 -0700 Subject: rcu: Make synchronize_srcu_expedited() fast if running readers The synchronize_srcu_expedited() function is currently quick if there are no active readers, but will delay a full jiffy if there are any. If these readers leave their SRCU read-side critical sections quickly, this is way too long to wait. So this commit first waits ten microseconds, and only then falls back to jiffy-at-a-time waiting. Reported-by: Avi Kivity Reported-by: Marcelo Tosatti Tested-by: Takuya Yoshikawa Signed-off-by: Paul E. McKenney --- kernel/srcu.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel/srcu.c') diff --git a/kernel/srcu.c b/kernel/srcu.c index c71e0750053..98d8c1e80ed 100644 --- a/kernel/srcu.c +++ b/kernel/srcu.c @@ -31,6 +31,7 @@ #include #include #include +#include #include static int init_srcu_struct_fields(struct srcu_struct *sp) @@ -203,9 +204,14 @@ static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void)) * all srcu_read_lock() calls using the old counters have completed. * Their corresponding critical sections might well be still * executing, but the srcu_read_lock() primitives themselves - * will have finished executing. + * 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. */ + if (srcu_readers_active_idx(sp, idx)) + udelay(CONFIG_SRCU_SYNCHRONIZE_DELAY); while (srcu_readers_active_idx(sp, idx)) schedule_timeout_interruptible(1); -- cgit v1.2.3-70-g09d2