| Date: Tue, 27 Oct 2015 07:31:53 -0500 |
| From: Josh Cartwright <joshc@ni.com> |
| Subject: net: Make synchronize_rcu_expedited() conditional on !RT_FULL |
| |
| 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 this change, we can observe a latency spike up to 30us with |
| cyclictest by rapidly unplugging/reestablishing an ethernet link. |
| |
| Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| Signed-off-by: Josh Cartwright <joshc@ni.com> |
| Cc: bigeasy@linutronix.de |
| Acked-by: Eric Dumazet <eric.dumazet@gmail.com> |
| Acked-by: David S. Miller <davem@davemloft.net> |
| Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| Link: http://lkml.kernel.org/r/20151027123153.GG8245@jcartwri.amer.corp.natinst.com |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| --- |
| net/core/dev.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/net/core/dev.c |
| +++ b/net/core/dev.c |
| @@ -7222,7 +7222,7 @@ EXPORT_SYMBOL(free_netdev); |
| void synchronize_net(void) |
| { |
| might_sleep(); |
| - if (rtnl_is_locked()) |
| + if (rtnl_is_locked() && !IS_ENABLED(CONFIG_PREEMPT_RT_FULL)) |
| synchronize_rcu_expedited(); |
| else |
| synchronize_rcu(); |