Messages in this thread | | | Date | Wed, 11 Jun 2014 12:48:32 -0700 | From | "Paul E. McKenney" <> | Subject | 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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On Wed, Jun 11, 2014 at 01:27:07PM -0500, Dave Chiluk wrote: > 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.
The solution might be to create such a beast. I might be able to shave a bit of time off of this benchmark, but at the cost of significant increases in RCU's CPU consumption. A bulk teardown/recreation API could reduce the RCU grace-period overhead by several orders of magnitude by having a single RCU grace period cover a few thousand changes.
This is why other bulk-change syscalls exist.
Just out of curiosity, what syscalls does the ip command use?
Thanx, Paul
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