[ovs-dev] ovn-controller is taking 100% CPU all the time in one deployment
Numan Siddique
nusiddiq at redhat.com
Thu Aug 29 18:39:50 UTC 2019
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
patch.
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 SB
DB IDL).
- 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
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