Hello Christian, Yes, I believe its related and I'm not sure why other bug was opened (other than this one). For now, lets concentrate efforts into this one only. I still need feedback from final user - present in the case discussion - and still need to do some more testing.
Somehow the best move here is a bisection and then the problem resolution (since we have a good and a bad version). We can try to guess the problem, but, unfortunately we can't reproduce at our side. Do have in mind that their setup is not using Canonical/Ubuntu OVS and DPDK, just QEMU. Jan, based on your comment: " One guest application where this problem is observed is a DPDK application using a pipeline of multiple DPDK logical cores to process packets between Rx from one virtio-net device and Tx to another virtio- net device. The DPDK lcores are coupled through DPDK rings that may buffer a significant amount of packets inside the application. " This is the reason I said: * Raising tx queue size make the flushes longer in time and that is possibly causing a bigger throughput (stopping the queue overrun). This tells us that either the buffer is smaller OR the flush is being called less times than it should (<- less scheduling or lock contention). For this other comment: " One possible explanation for the observed changed behavior in Qemu 2.5 compared to Qemu 2.3 could be that for some reason one of these DPDK threads is interrupted so that a significant amount of packets queue up in its ingress ring. These are then forwarded in a burst at larger speed than normal to the Tx virtio queue. This would imply that Qemu 2.5 changes the scheduling of such DPDK threads in the guest. " * Yep, the "some reason" for the interruption of dpdk threads scheduling is the problem I would like to pursue - like said in the first comment. Do have in mind that it might not have anything related to virtio or vhost, but, something that causes the timer function callback to be postponed (example). I'll comment the vhost queue comment in the next one. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1668829 Title: Performance regression from qemu 2.3 to 2.5 for vhost-user with ovs + dpdk To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1668829/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
