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Date:	Sun, 08 May 2011 10:35:02 +0100
From:	Alex Bligh <alex@...x.org.uk>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	netdev@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Alex Bligh <alex@...x.org.uk>
Subject: Re: Scalability of interface creation and deletion

Eric,

--On 8 May 2011 09:12:22 +0200 Eric Dumazet <eric.dumazet@...il.com> wrote:

> By the way, if I change HZ from 1000 to 100 I now have ten times slower
> result :

I repeated that test here. With HZ set to 1000 I got a total time of
4.022 seconds to remove 100 interfaces, of which:

 Total 3.03808 Usage 199 Average 0.01527 elsewhere
 Total 0.93992 Usage 200 Average 0.00470 synchronizing

as opposed to a total of 27.917 seconds with HZ set to 100, of which

 Total 18.98515 Usage 199 Average 0.09540 elsewhere
 Total 8.77581 Usage 200 Average 0.04388 synchronizing

Not quite a factor of 10 improvement, but nearly.

I have CONFIG_RCU_FAST_NO_HZ=y

I suspect this may just mean an rcu reader holds the rcu_read_lock
for a jiffies related time. Though I'm having difficulty seeing
what that might be on a system where the net is in essence idle.

-- 
Alex Bligh
--
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