path: root/kernel
diff options
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-01-07 02:33:47 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2011-01-14 04:56:49 -0800
commitc072a388d59a1d48e36864d0e66f42d71745be1c (patch)
treea0537c767c834d1846430ab3bb4eb83c0d0923d7 /kernel
parent394f4528c523d88daabd50f883a8d6b164075555 (diff)
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 <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
1 files changed, 13 insertions, 2 deletions
diff --git a/kernel/srcu.c b/kernel/srcu.c
index 98d8c1e80ed..73ce23feaea 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -156,6 +156,16 @@ void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+ * 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.
+ */
* Helper function for synchronize_srcu() and synchronize_srcu_expedited().
static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
@@ -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))
while (srcu_readers_active_idx(sp, idx))