[ovs-discuss] ovn-controller is taking 100% CPU all the time in one deployment

Han Zhou zhouhan at gmail.com
Thu Aug 29 19:07:27 UTC 2019

On Thu, Aug 29, 2019 at 11:40 AM Numan Siddique <nusiddiq at redhat.com> wrote:
> Hello Everyone,
> In one of the OVN deployments, we are seeing 100% CPU usage by
ovn-controllers all the time.
> After investigations we found the below
>  - ovn-controller is taking more than 20 seconds to complete full loop
(mainly in lflow_run() function)
>  - The physical switch is sending GARPs periodically every 10 seconds.
>  - There is ovn-bridge-mappings configured and these GARP packets reaches
br-int via the patch port.
>  - We have a flow in router pipeline which applies the action - put_arp
> if it is arp packet.
>  - ovn-controller pinctrl thread receives these garps, stores the learnt
mac-ips in the 'put_mac_bindings' hmap and notifies the ovn-controller main
thread by incrementing the seq no.
>  - In the ovn-controller main thread, after lflow_run() finishes,
pinctrl_wait() is called. This function calls - poll_immediate_wake() as
'put_mac_bindings' hmap is not empty.
> - This causes the ovn-controller poll_block() to not sleep at all and
this repeats all the time resulting in 100% cpu usage.
> The deployment has OVS/OVN 2.9.  We have back ported the pinctrl_thread
> Some time back I had reported an issue about lflow_run() taking lot of
time - https://mail.openvswitch.org/pipermail/ovs-dev/2019-July/360414.html
> I think we need to improve the logical processing sooner or later.
> But to fix this issue urgently, we are thinking of the below approach.
>  - pinctrl_thread will locally cache the mac_binding entries (just like
it caches the dns entries). (Please note pinctrl_thread can not access the
> - Upon receiving any arp packet (via the put_arp action), pinctrl_thread
will check the local mac_binding cache and will only wake up the main
ovn-controller thread only if the mac_binding update is required.
> This approach will solve the issue since the MAC sent by the physical
switches will not change. So there is no need to wake up ovn-controller
main thread.
> In the present master/2.12 these GARPs will not cause this 100% cpu loop
issue because incremental processing will not recompute flows.
> Even though the above approach is not really required for master/2.12, I
think it is still Ok to have this as there is no harm.
> I would like to know your comments and any concerns if any.
> Thanks
> Numan

Hi Numan,

I think this approach should work. Just to make sure, to update the cache
efficiently (to avoid another kind of recompute), it should use ovsdb
change-tracking to update it incrementally.

Regarding master/2.12, it is not harmful except that it will add some more
code and increase memory footprint. For our current use cases, there can be
easily 10,000s mac_bindings, but it may still be ok because each entry is
very small. However, is there any benefit for doing this in master/2.12?

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