netdev - Re: Testing interface removal speedup patches from Eric Dumazet.

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Message-ID: <D8B72070C6338973B87C9EFA@Ximines.local>
Date:	Mon, 09 May 2011 20:12:39 +0100
From:	Alex Bligh <alex@...x.org.uk>
To:	Ben Greear <greearb@...delatech.com>
cc:	netdev <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Alex Bligh <alex@...x.org.uk>
Subject: Re: Testing interface removal speedup patches from Eric Dumazet.



--On 9 May 2011 12:02:47 -0700 Ben Greear <greearb@...delatech.com> wrote:


>> So Eric's patches help in the interface create case, even though
>> there is no synchronize_net, sychronize_sched() or rcu_barrier() there.
>>
>> I had assumed the slow create (which varies by number of pairs) was
>> down to sysfs scalability only (see difference between 14ms and 110ms
>> there).
>
> I'm not certain the create case is actually faster.  Other runs on the
> patched kernel showed create to be much closer to the un-patched kernel.
>
> The ratios to create/delete are more consistent it seems.
>
>> Out of interest, if you still happen to have the scripts around, how
>> fast is veth creation if you just do 100 pairs?
>
> Created 500 veth in 17.874695 seconds (0.03574939 per interface).
> Created 100 veth in 2.779905 seconds (0.02779905 per interface).

Hmmm... well you are getting *far* better linearity than me. Creating
500 interfaces is 8 times slower *per interface* than doing 500.

What occurs to me is that your box is faster than one of the ones I tested
on, and you use CONFIG_HZ=100 but you get poorer results in absolute terms
doing 100 (I see 14ms per interface). This with everything listenting to
udev disabled? (so udevd dead, whatever executes your ifup/down scripts
dead, unshare -n).

-- 
Alex Bligh
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