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| author |   Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-11 16:24:45 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2015-07-17 14:59:06 -0700 |
| commit | cdacbe1f91264687af956e810278030f2ab5a3d0 (patch) | |
| tree | 3a4e912e5c319329bc2a1e68b99ee041f0777150 /kernel/rcu | |
| parent | rcu: Rename RCU_GP_DONE_FQS to RCU_GP_DOING_FQS (diff) | |
| download | linux-dev-cdacbe1f91264687af956e810278030f2ab5a3d0.tar.xz linux-dev-cdacbe1f91264687af956e810278030f2ab5a3d0.zip | |
rcu: Add fastpath bypassing funnel locking
In the common case, there will be only one expedited grace period in
the system at a given time, in which case it is not helpful to use
funnel locking. This commit therefore adds a fastpath that bypasses
funnel locking when the root ->exp_funnel_mutex is not held.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 16 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 2 | ||||
| -rw-r--r-- | kernel/rcu/tree_trace.c | 4 |
3 files changed, 19 insertions, 3 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f66f6e7730bc..3af0dee2d045 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3356,6 +3356,22 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s) struct rcu_node *rnp1 = NULL; /* + * First try directly acquiring the root lock in order to reduce + * latency in the common case where expedited grace periods are + * rare. We check mutex_is_locked() to avoid pathological levels of + * memory contention on ->exp_funnel_mutex in the heavy-load case. + */ + rnp0 = rcu_get_root(rsp); + if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) { + if (mutex_trylock(&rnp0->exp_funnel_mutex)) { + if (sync_exp_work_done(rsp, rnp0, NULL, + &rsp->expedited_workdone0, s)) + return NULL; + return rnp0; + } + } + + /* * Each pass through the following loop works its way * up the rcu_node tree, returning if others have done the * work or otherwise falls through holding the root rnp's diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 543ba726396c..80d974df0ea0 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -493,7 +493,7 @@ struct rcu_state { /* End of fields guarded by barrier_mutex. */ unsigned long expedited_sequence; /* Take a ticket. */ - atomic_long_t expedited_tryfail; /* # acquisition failures. */ + atomic_long_t expedited_workdone0; /* # done by others #0. */ atomic_long_t expedited_workdone1; /* # done by others #1. */ atomic_long_t expedited_workdone2; /* # done by others #2. */ atomic_long_t expedited_workdone3; /* # done by others #3. */ diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c index ec62369f1b02..6fc4c5ff3bb5 100644 --- a/kernel/rcu/tree_trace.c +++ b/kernel/rcu/tree_trace.c @@ -185,9 +185,9 @@ static int show_rcuexp(struct seq_file *m, void *v) { struct rcu_state *rsp = (struct rcu_state *)m->private; - seq_printf(m, "t=%lu tf=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", + seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n", rsp->expedited_sequence, - atomic_long_read(&rsp->expedited_tryfail), + atomic_long_read(&rsp->expedited_workdone0), atomic_long_read(&rsp->expedited_workdone1), atomic_long_read(&rsp->expedited_workdone2), atomic_long_read(&rsp->expedited_workdone3), |