From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Cartwright Subject: [PATCH -rt] Revert "net: use synchronize_rcu_expedited()" Date: Mon, 26 Oct 2015 14:14:55 -0500 Message-ID: <1445886895-3692-1-git-send-email-joshc@ni.com> Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Dumazet , "Paul E. McKenney" , "David S. Miller" To: tglx@linutronix.de, bigeasy@linutronix.de Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org 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 Cc: Paul E. McKenney Cc: David S. Miller Signed-off-by: Josh Cartwright --- 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) { might_sleep(); - if (rtnl_is_locked()) - synchronize_rcu_expedited(); - else - synchronize_rcu(); + synchronize_rcu(); } EXPORT_SYMBOL(synchronize_net); -- 2.5.1