linux-kernel - Re: Possible netns creation and execution performance/scalability regression since v3.8 due to rcu callbacks being offloaded to multiple cpus

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Date:	Wed, 11 Jun 2014 13:27:07 -0500
From:	Dave Chiluk <chiluk@...onical.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Rafael Tinoco <rafael.tinoco@...onical.com>,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	ebiederm@...ssion.com,
	Christopher Arges <chris.j.arges@...onical.com>,
	Jay Vosburgh <jay.vosburgh@...onical.com>
Subject: Re: Possible netns creation and execution performance/scalability
 regression since v3.8 due to rcu callbacks being offloaded to multiple cpus

On 06/11/2014 11:18 AM, Paul E. McKenney wrote:
> On Wed, Jun 11, 2014 at 10:46:00AM -0500, David Chiluk wrote:
>> Now think about what happens when a gateway goes down, the namespaces
>> need to be migrated, or a new machine needs to be brought up to replace
>> it.  When we're talking about 3000 namespaces, the amount of time it
>> takes simply to recreate the namespaces becomes very significant.
>>
>> The script is a stripped down example of what exactly is being done on
>> the neutron gateway in order to create namespaces.
> 
> Are the namespaces torn down and recreated one at a time, or is there some
> syscall, ioctl(), or whatever that allows bulk tear down and recreating?
> 
> 							Thanx, Paul

In the normal running case, the namespaces are created one at a time, as
new customers create a new set of VMs on the cloud.

However, in the case of failover to a new neutron gateway the namespaces
are created all at once using the ip command (more or less serially).

As far as I know there is no syscall or ioctl that allows bulk tear down
and recreation.  if such a beast exists that might be helpful.


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