diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-07-26 20:47:42 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-08-20 11:45:50 -0700 |
| commit | 458fb381eacdd23366cfa2fbdf5a467848683e3a (patch) | |
| tree | 2e99312defa53ba0576e303021a0a2bf62b664b8 /kernel/rcutree.c | |
| parent | 5361471437a97cf493c2aa7d881bbedc9c248415 (diff) | |
rcu: Simplify _rcu_barrier() processing
This commit drops an unneeded ACCESS_ONCE() and simplifies an "our work
is done" check in _rcu_barrier(). This applies feedback from Linus
(https://lkml.org/lkml/2013/7/26/777) that he gave to similar code
in an unrelated patch.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
[ paulmck: Fix comment to match code, reported by Lai Jiangshan. ]
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index c6a064abd6a..a4a04f311cf 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2817,9 +2817,20 @@ static void _rcu_barrier(struct rcu_state *rsp) * transition. The "if" expression below therefore rounds the old * value up to the next even number and adds two before comparing. */ - snap_done = ACCESS_ONCE(rsp->n_barrier_done); + snap_done = rsp->n_barrier_done; _rcu_barrier_trace(rsp, "Check", -1, snap_done); - if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) { + + /* + * If the value in snap is odd, we needed to wait for the current + * rcu_barrier() to complete, then wait for the next one, in other + * words, we need the value of snap_done to be three larger than + * the value of snap. On the other hand, if the value in snap is + * even, we only had to wait for the next rcu_barrier() to complete, + * in other words, we need the value of snap_done to be only two + * greater than the value of snap. The "(snap + 3) & ~0x1" computes + * this for us (thank you, Linus!). + */ + if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) { _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rsp->barrier_mutex); |