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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-04-11 00:40:35 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-06-08 17:25:22 +0200 |
| commit | f92c734f02cbf10e40569facff82059ae9b61920 (patch) | |
| tree | 95d64d71c63d840d31bef62793ce8262305a6f1e | |
| parent | rcutorture: Add a scenario for Classic SRCU (diff) | |
| download | linux-f92c734f02cbf10e40569facff82059ae9b61920.tar.xz linux-f92c734f02cbf10e40569facff82059ae9b61920.zip | |
rcu: Prevent rcu_barrier() from starting needless grace periods
Currently rcu_barrier() uses call_rcu() to enqueue new callbacks
on each CPU with a non-empty callback list. This works, but means
that rcu_barrier() forces grace periods that are not otherwise needed.
The key point is that rcu_barrier() never needs to wait for a grace
period, but instead only for all pre-existing callbacks to be invoked.
This means that rcu_barrier()'s new callbacks should be placed in
the callback-list segment containing the last pre-existing callback.
This commit makes this change using the new rcu_segcblist_entrain()
function.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
| -rw-r--r-- | include/trace/events/rcu.h | 1 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 10 |
2 files changed, 9 insertions, 2 deletions
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index e3facb356838..91dc089d65b7 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -742,6 +742,7 @@ TRACE_EVENT(rcu_torture_read, * "OnlineQ": _rcu_barrier() found online CPU with callbacks. * "OnlineNQ": _rcu_barrier() found online CPU, no callbacks. * "IRQ": An rcu_barrier_callback() callback posted on remote CPU. + * "IRQNQ": An rcu_barrier_callback() callback found no callbacks. * "CB": An rcu_barrier_callback() invoked a callback, not the last. * "LastCB": An rcu_barrier_callback() invoked the last callback. * "Inc2": _rcu_barrier() piggyback check counter incremented. diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e354e475e645..657056c3e0cd 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3578,8 +3578,14 @@ static void rcu_barrier_func(void *type) struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); _rcu_barrier_trace(rsp, "IRQ", -1, rsp->barrier_sequence); - atomic_inc(&rsp->barrier_cpu_count); - rsp->call(&rdp->barrier_head, rcu_barrier_callback); + rdp->barrier_head.func = rcu_barrier_callback; + debug_rcu_head_queue(&rdp->barrier_head); + if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) { + atomic_inc(&rsp->barrier_cpu_count); + } else { + debug_rcu_head_unqueue(&rdp->barrier_head); + _rcu_barrier_trace(rsp, "IRQNQ", -1, rsp->barrier_sequence); + } } /* |