[PATCH -rt] Revert "net: use synchronize_rcu_expedited()"

From: Josh Cartwright
Date: Mon Oct 26 2015 - 15:15:16 EST

This reverts commit be3fc413da9eb17cce0991f214ab019d16c88c41.

While the use of synchronize_rcu_expedited() might make
synchronize_net() "faster", it does so at significant cost on RT
systems, as expediting a grace period forcibly preempts any
high-priority RT tasks (via the stop_machine() mechanism).

Without be3fc413da9e reverted, we can observe a latency spike up to 30us
with cyclictest by rapidly unplugging/reestablishing an ethernet link.

Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Josh Cartwright <joshc@xxxxxx>
net/core/dev.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f8c23de..869ef62 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6969,10 +6969,7 @@ EXPORT_SYMBOL(free_netdev);
void synchronize_net(void)
- if (rtnl_is_locked())
- synchronize_rcu_expedited();
- else
- synchronize_rcu();
+ synchronize_rcu();


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