netdev - Re: [PATCHv3] virtio-spec: virtio network device multiqueue support

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Date:	Fri, 7 Sep 2012 03:26:03 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Jason Wang <jasowang@...hat.com>, rusty@...tcorp.com.au,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCHv3] virtio-spec: virtio network device multiqueue support

On Fri, Sep 07, 2012 at 02:17:08AM +0200, Sasha Levin wrote:
> Hi Michael,
> 
> On 09/06/2012 02:08 PM, Michael S. Tsirkin wrote:
> > Add multiqueue support to virtio network device.
> > Add a new feature flag VIRTIO_NET_F_MULTIQUEUE for this feature, a new
> > configuration field max_virtqueue_pairs to detect supported number of
> > virtqueues as well as a new command VIRTIO_NET_CTRL_STEERING to program
> > packet steering.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> 
> Some comments about the change:
> 
>  - "The following four read-only fields only exists if VIRTIO_NET_F_MULTIQUEUE
> is set." => Should be "exist" (I think).
> 
>  - "When rule is set to VIRTIO_NET_CTRL_STEERING_RX_FOLLOWS_TX packets are
> steered by driver to the first (param+1) multiqueue virtqueues
> transmitq1...transmitqN;" - Why param+1?  I thought we ignore the default
> transmit/receive in this case.

This is so that all values are valid. E.g. param=0 -> use q1.

> 
>  - "As selecting a specific steering ais n optimization feature" - "is an".
> 
>  - It's mentioned several times that the ability to read the steering rule from
> the virtio-net config is there for debug reasons. Is it really necessary? I
> think it's the first time I see debug features go in as part of the spec.

I actually think we need to work on more debug features.

>  - I'm slightly confused, why are there both receive and transmit steering? I
> can't find a difference in the way to configure the rule for transmit and
> receive. Is it a plan for the future to allow different rules for tx and rx? If
> so, shouldn't we use different ctrl commands (
> VIRTIO_NET_CTRL_TX_STEERING/VIRTIO_NET_CTRL_RX_STEERING)?

No. Receive steering is done by device. Documented for driver writer's
benefit. xmit streering by driver. documented for device benefit.
They must match for tcp to work well so I doubt we will have
commands to control them separately.

>  - "When rule is set to VIRTIO_NET_CTRL_STEERING_SINGLE all packets are steered
> to the default virtqueue receveq (0);" - "receiveq (0)"
> 
> 
> 
> Thanks,
> Sasha


Thanks for the comments will address!

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