netdev - Re: [net-next RFC V5 4/5] virtio

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Message-ID: <500CE72B.2040101@redhat.com>
Date:	Mon, 23 Jul 2012 13:54:51 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Sasha Levin <levinsasha928@...il.com>
CC:	"Michael S. Tsirkin" <mst@...hat.com>, mashirle@...ibm.com,
	krkumar2@...ibm.com, habanero@...ux.vnet.ibm.com,
	rusty@...tcorp.com.au, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, edumazet@...gle.com,
	tahm@...ux.vnet.ibm.com, jwhan@...ewood.snu.ac.kr,
	davem@...emloft.net, akong@...hat.com, kvm@...r.kernel.org,
	sri@...ibm.com
Subject: Re: [net-next RFC V5 4/5] virtio_net: multiqueue support

On 07/21/2012 08:02 PM, Sasha Levin wrote:
> On 07/20/2012 03:40 PM, Michael S. Tsirkin wrote:
>>> -	err = init_vqs(vi);
>>>> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
>>>> +		vi->has_cvq = true;
>>>> +
>> How about we disable multiqueue if there's no cvq?
>> Will make logic a bit simpler, won't it?
> multiqueues don't really depend on cvq. Does this added complexity really justifies adding an artificial limit?
>

Yes, it does not depends on cvq. Cvq were just used to negotiate the 
number of queues a guest wishes to use which is really useful (at least 
for now). Since multiqueue can not out-perform for single queue in every 
kinds of workloads or benchmark, so we want to let guest driver use 
single queue by default even when multiqueue were enabled by management 
software and let use to enalbe it through ethtool. So user could not 
feel regression when it switch to use a multiqueue capable driver and 
backend.

So the only difference is the user experiences.
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