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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-03-16 13:22:53 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2016-03-31 13:34:09 -0700
commit356051e1de3cf65575da4ee92d1f5cee86677ee2 (patch)
tree498fde3d22598558fc41ce20ebfb183d014b9c4f /kernel/rcu
parentf6a12f34a448cc8a624070fd365c29c890138a48 (diff)
downloadlinux-sh-356051e1de3cf65575da4ee92d1f5cee86677ee2.tar.gz
rcu: Add exp_funnel_lock() fastpath
This commit speeds up the low-contention case, especially for systems with large rcu_node trees, by attempting to directly acquire the ->exp_mutex. This fastpath checks the leaves and root first in order to avoid excessive memory contention on the mutex itself. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index bd2658edce00..892a140ae7b6 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3603,6 +3603,15 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
{
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
struct rcu_node *rnp = rdp->mynode;
+ struct rcu_node *rnp_root = rcu_get_root(rsp);
+
+ /* Low-contention fastpath. */
+ if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
+ (rnp == rnp_root ||
+ ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
+ !mutex_is_locked(&rsp->exp_mutex) &&
+ mutex_trylock(&rsp->exp_mutex))
+ goto fastpath;
/*
* Each pass through the following loop works its way up
@@ -3635,6 +3644,7 @@ static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
rnp->grphi, TPS("nxtlvl"));
}
mutex_lock(&rsp->exp_mutex);
+fastpath:
if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
mutex_unlock(&rsp->exp_mutex);
return true;