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

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Message-ID: <50493D04.1090408@gmail.com>
Date:	Fri, 07 Sep 2012 02:17:08 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.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

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.

 - "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'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)?

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



Thanks,
Sasha
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