On Tue, 2011-11-15 at 10:14 +0530, Krishna Kumar2 wrote:

Sasha Levin [off-list ref] wrote on 11/14/2011 03:45:40 PM:

quoted

quoted

Why both the bandwidth and latency performance are dropping so
dramatically with multiple VQ?

It looks like theres no hash sync between host and guest, which makes
the RX VQ change for every packet. This is my guess.

Yes, I confirmed this happens for macvtap. I am
using ixgbe - it calls skb_record_rx_queue when
a skb is allocated, but sets rxhash when a packet
arrives. Macvtap is relying on record_rx_queue
first ahead of rxhash (as part of my patch making
macvtap multiqueue), hence different skbs result
in macvtap selecting different vq's.

I'm seeing this behavior in non-macvtep related setup as well (simple
tap <-> virtio-net).

-- 

Sasha.