Messages in this thread | | | From | Christian Brauner <> | Date | Fri, 20 Apr 2018 18:16:44 +0200 | Subject | Re: [PATCH net-next 2/2] netns: isolate seqnums to use per-netns locks |
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On Fri, Apr 20, 2018 at 03:56:28PM +0200, Christian Brauner wrote: > On Wed, Apr 18, 2018 at 11:52:47PM +0200, Christian Brauner wrote: > > On Wed, Apr 18, 2018 at 11:55:52AM -0500, Eric W. Biederman wrote: > > > Christian Brauner <christian.brauner@ubuntu.com> writes: > > > > > > > Now that it's possible to have a different set of uevents in different > > > > network namespaces, per-network namespace uevent sequence numbers are > > > > introduced. This increases performance as locking is now restricted to the > > > > network namespace affected by the uevent rather than locking > > > > everything. > > > > > > Numbers please. I personally expect that the netlink mc_list issues > > > will swamp any benefit you get from this. > > > > I wouldn't see how this would be the case. The gist of this is: > > Everytime you send a uevent into a network namespace *not* owned by > > init_user_ns you currently *have* to take mutex_lock(uevent_sock_list) > > effectively blocking the host from processing uevents even though > > - the uevent you're receiving might be totally different from the > > uevent that you're sending > > - the uevent socket of the non-init_user_ns owned network namespace > > isn't even recorded in the list. > > > > The other argument is that we now have properly isolated network > > namespaces wrt to uevents such that each netns can have its own set of > > uevents. This can either happen by a sufficiently privileged userspace > > process sending it uevents that are only dedicated to that specific > > netns. Or - and this *has been true for a long time* - because network > > devices are *properly namespaced*. Meaning a uevent for that network > > device is *tied to a network namespace*. For both cases the uevent > > sequence numbering will be absolutely misleading. For example, whenever > > you create e.g. a new veth device in a new network namespace it > > shouldn't be accounted against the initial network namespace but *only* > > against the network namespace that has that device added to it. > > Eric, I did the testing. Here's what I did: > > I compiled two 4.17-rc1 Kernels: > - one with per netns uevent seqnums with decoupled locking > - one without per netns uevent seqnums with decoupled locking > > # Testcase 1: > Only Injecting Uevents into network namespaces not owned by the initial user > namespace. > - created 1000 new user namespace + network namespace pairs > - opened a uevent listener in each of those namespace pairs > - injected uevents into each of those network namespaces 10,000 times meaning > 10,000,000 (10 million) uevents were injected. (The high number of > uevent injections should get rid of a lot of jitter.) > - Calculated the mean transaction time. > - *without* uevent sequence number namespacing: > 67 μs > - *with* uevent sequence number namespacing: > 55 μs > - makes a difference of 12 μs > > # Testcase 2: > Injecting Uevents into network namespaces not owned by the initial user > namespace and network namespaces owned by the initial user namespace. > - created 500 new user namespace + network namespace pairs > - created 500 new network namespace pairs > - opened a uevent listener in each of those namespace pairs > - injected uevents into each of those network namespaces 10,000 times meaning > 10,000,000 (10 million) uevents were injected. (The high number of > uevent injections should get rid of a lot of jitter.) > - Calculated the mean transaction time. > - *without* uevent sequence number namespacing: > 572 μs > - *with* uevent sequence number namespacing: > 514 μs > - makes a difference of 58 μs > > So there's performance gain. The third case would be to create a bunch > of hanging processes that send SIGSTOP to themselves but do not actually > open a uevent socket in their respective namespaces and then inject > uevents into them. I expect there to be an even more performance > benefits since the rtnl_table_lock() isn't hit in this case because > there are no listeners.
I did the third test-case as well so: - created 500 new user namespace + network namespace pairs *without uevent listeners* - created 500 new network namespace pairs *without uevent listeners* - injected uevents into each of those network namespaces 10,000 times meaning 10,000,000 (10 million) uevents were injected. (The high number of uevent injections should get rid of a lot of jitter.) - Calculated the mean transaction time. - *without* uevent sequence number namespacing: 206 μs - *with* uevent sequence number namespacing: 163 μs - makes a difference of 43 μs
So this test-case shows performance improvement as well.
Thanks! Christian
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