netdev - Re: BUG ? ipip unregister_netdevice

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Date:	Thu, 14 Oct 2010 22:21:02 +0300
From:	"Octavian Purdila" <opurdila@...acom.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"David Miller" <davem@...emloft.net>
Cc:	<hans.schillstrom@...csson.com>, <daniel.lezcano@...e.fr>,
	<netdev@...r.kernel.org>
Subject: Re: BUG ? ipip unregister_netdevice_many()


> > How can it make a real difference even in this case? We'll obliterate
> > all the entries, and then on subsequent passes we'll find nothing
> > matching that namespace any more.
> > 
> > Show me performance tests that show it makes any difference, please.
> 
> Octavian did you happen to measure the performance difference when you
> added batching of routing table flushes?
> 

Unfortunatelly I dont't have the numbers anymore, but I remember it was noticeable when using a large number of interfaces (10K) - if I remember correctly around 1 second out of 10 for the whole unregister process.

BTW, another bottleneck for mass unregister while interfaces are up is dev_deactivate / dev_close. I experimented with "batchifying" it and for 32K interfaces the time went down from 5mins to 30s.

The patch I have is not pretty, it basically creates another 2 functions for each of dev_close and dev_deactivate for pre and post synchronise_rcu barrier.
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