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Date: Sun, 08 May 2011 14:06:07 +0100 From: Alex Bligh <alex@...x.org.uk> To: paulmck@...ux.vnet.ibm.com cc: Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org, Alex Bligh <alex@...x.org.uk> Subject: Re: Scalability of interface creation and deletion --On 8 May 2011 05:44:28 -0700 "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote: > OK, let's break it out... > > 4.022 seconds for 100 interfaces means about 40 milliseconds per > interface. It's 200 interfaces as they are veth pairs, so 20ms. > My guess is that you have CONFIG_NO_HZ=y, which means that RCU needs to > figure out that various CPUs are in dyntick-idle state, which is a minimum > of 6 jiffies. That sounds like the main cause. > It could be longer if a given CPU happens to be in IRQ > when RCU checks, so call it 9 jiffies. That sounds unlikely to happen much of the time. Looking at /proc/interrupts not much is going on. > If you are doing the interfaces > synchronously, you will likely have to wait for a prior grace period (due > to background activity). Not sure I understand that (there's nothing else going on), but... > So I can easily imagine 18 milliseconds for > HZ=1000. 40 milliseconds sounds a bit high, but perhaps not impossible. Add to that the fact that there are 2 x synchronize_sched() and one rcu_barrier() per interface removal. If I ignore your IRQ idea, that's 6 x 3 = 18ms per interface removal at CONFIG_HZ=10, 180ms at CONFIG_HZ=100. -- Alex Bligh -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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