Re: vhost + multiqueue + RSS question.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.

The point is to try and take application locality into account.


> --
> 			Gleb.
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization




[Index of Archives]     [KVM Development]     [Libvirt Development]     [Libvirt Users]     [CentOS Virtualization]     [Netdev]     [Ethernet Bridging]     [Linux Wireless]     [Kernel Newbies]     [Security]     [Linux for Hams]     [Netfilter]     [Bugtraq]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]

  Powered by Linux