From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sasha Levin <levinsasha928@gmail.com>
Subject: Re: [RFC] kvm tools: Implement multiple VQ for virtio-net
Date: Tue, 15 Nov 2011 17:30:29 +0200
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Cc: Asias He <asias.hejun@gmail.com>, gorcunov@gmail.com,
	kvm@vger.kernel.org, mingo@elte.hu,
	"Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org,
	penberg@kernel.org, Rusty Russell <rusty@rustcorp.com.au>,
	virtualization@lists.linux-foundation.org
To: Krishna Kumar2 <krkumar2@in.ibm.com>
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On Tue, 2011-11-15 at 10:14 +0530, Krishna Kumar2 wrote:
> Sasha Levin <levinsasha928@gmail.com> wrote on 11/14/2011 03:45:40 PM:
> 
> > > 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.