From be3fc413da9eb17cce0991f214ab019d16c88c41 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 23 May 2011 23:07:32 +0000 Subject: [PATCH] net: use synchronize_rcu_expedited() synchronize_rcu() is very slow in various situations (HZ=100, CONFIG_NO_HZ=y, CONFIG_PREEMPT=n) Extract from my (mostly idle) 8 core machine : synchronize_rcu() in 99985 us synchronize_rcu() in 79982 us synchronize_rcu() in 87612 us synchronize_rcu() in 79827 us synchronize_rcu() in 109860 us synchronize_rcu() in 98039 us synchronize_rcu() in 89841 us synchronize_rcu() in 79842 us synchronize_rcu() in 80151 us synchronize_rcu() in 119833 us synchronize_rcu() in 99858 us synchronize_rcu() in 73999 us synchronize_rcu() in 79855 us synchronize_rcu() in 79853 us When we hold RTNL mutex, we would like to spend some cpu cycles but not block too long other processes waiting for this mutex. We also want to setup/dismantle network features as fast as possible at boot/shutdown time. This patch makes synchronize_net() call the expedited version if RTNL is locked. synchronize_rcu_expedited() typical delay is about 20 us on my machine. synchronize_rcu_expedited() in 18 us synchronize_rcu_expedited() in 18 us synchronize_rcu_expedited() in 18 us synchronize_rcu_expedited() in 18 us synchronize_rcu_expedited() in 20 us synchronize_rcu_expedited() in 16 us synchronize_rcu_expedited() in 20 us synchronize_rcu_expedited() in 18 us synchronize_rcu_expedited() in 18 us Signed-off-by: Eric Dumazet CC: Paul E. McKenney CC: Ben Greear Reviewed-by: Paul E. McKenney Signed-off-by: David S. Miller --- net/core/dev.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/core/dev.c b/net/core/dev.c index bcb05cb799c1..ec11d757c1fc 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -5954,7 +5954,10 @@ EXPORT_SYMBOL(free_netdev); void synchronize_net(void) { might_sleep(); - synchronize_rcu(); + if (rtnl_is_locked()) + synchronize_rcu_expedited(); + else + synchronize_rcu(); } EXPORT_SYMBOL(synchronize_net); -- 2.39.5