On Tue, Nov 18, 2014 at 11:41:11AM +0800, Jason Wang wrote: > On 11/18/2014 09:37 AM, Zhang Haoyu wrote: > >> On Mon, Nov 17, 2014 at 01:58:20PM +0200, Michael S. Tsirkin wrote: > >>> On Mon, Nov 17, 2014 at 01:22:07PM +0200, Gleb Natapov wrote: > >>>> On Mon, Nov 17, 2014 at 12:38:16PM +0200, Michael S. Tsirkin wrote: > >>>>> On Mon, Nov 17, 2014 at 09:44:23AM +0200, Gleb Natapov wrote: > >>>>>> On Sun, Nov 16, 2014 at 08:56:04PM +0200, Michael S. Tsirkin wrote: > >>>>>>> On Sun, Nov 16, 2014 at 06:18:18PM +0200, Gleb Natapov wrote: > >>>>>>>> Hi Michael, > >>>>>>>> > >>>>>>>> I am playing with vhost multiqueue capability and have a question about > >>>>>>>> vhost multiqueue and RSS (receive side steering). My setup has Mellanox > >>>>>>>> ConnectX-3 NIC which supports multiqueue and RSS. Network related > >>>>>>>> parameters for qemu are: > >>>>>>>> > >>>>>>>> -netdev tap,id=hn0,script=qemu-ifup.sh,vhost=on,queues=4 > >>>>>>>> -device virtio-net-pci,netdev=hn0,id=nic1,mq=on,vectors=10 > >>>>>>>> > >>>>>>>> In a guest I ran "ethtool -L eth0 combined 4" to enable multiqueue. > >>>>>>>> > >>>>>>>> I am running one tcp stream into the guest using iperf. Since there is > >>>>>>>> only one tcp stream I expect it to be handled by one queue only but > >>>>>>>> this seams to be not the case. ethtool -S on a host shows that the > >>>>>>>> stream is handled by one queue in the NIC, just like I would expect, > >>>>>>>> but in a guest all 4 virtio-input interrupt are incremented. Am I > >>>>>>>> missing any configuration? > >>>>>>> I don't see anything obviously wrong with what you describe. > >>>>>>> Maybe, somehow, same irqfd got bound to multiple MSI vectors? > >>>>>> It does not look like this is what is happening judging by the way > >>>>>> interrupts are distributed between queues. They are not distributed > >>>>>> uniformly and often I see one queue gets most interrupt and others get > >>>>>> much less and then it changes. > >>>>> Weird. It would happen if you transmitted from multiple CPUs. > >>>>> You did pin iperf to a single CPU within guest, did you not? > >>>>> > >>>> No, I didn't because I didn't expect it to matter for input interrupts. > >>>> When I run iperf on a host rx queue that receives all packets depends > >>>> only on a connection itself, not on a cpu iperf is running on (I tested > >>>> that). > >>> This really depends on the type of networking card you have > >>> on the host, and how it's configured. > >>> > >>> I think you will get something more closely resembling this > >>> behaviour if you enable RFS in host. > >>> > >>>> When I pin iperf in a guest I do indeed see that all interrupts > >>>> are arriving to the same irq vector. Is a number after virtio-input > >>>> in /proc/interrupt any indication of a queue a packet arrived to (on > >>>> a host I can use ethtool -S to check what queue receives packets, but > >>>> unfortunately this does not work for virtio nic in a guest)? > >>> I think it is. > >>> > >>>> Because if > >>>> it is the way RSS works in virtio is not how it works on a host and not > >>>> what I would expect after reading about RSS. The queue a packets arrives > >>>> to should be calculated by hashing fields from a packet header only. > >>> Yes, what virtio has is not RSS - it's an accelerated RFS really. > >>> > >> OK, if what virtio has is RFS and not RSS my test results make sense. > >> Thanks! > > I think the RSS emulation for virtio-mq NIC is implemented in tun_select_queue(), > > am I missing something? > > > > Thanks, > > Zhang Haoyu > > > > Yes, if RSS is the short for Receive Side Steering which is a generic > technology. But RSS is usually short for Receive Side Scaling which was > commonly technology used by Windows, it was implemented through a > indirection table in the card which is obviously not supported in tun > currently. Hmm, I had an impression that "Receive Side Steering" and "Receive Side Scaling" are interchangeable. Software implementation for RSS is called "Receive Packet Steering" according to Documentation/networking/scaling.txt not "Receive Packet Scaling". Those damn TLAs are confusing. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
