Re: [Qemu-devel] [PATCH v1] virtio-net: enable configurable tx queue size

[Michael S. Tsirkin]

On Mon, Jun 05, 2017 at 10:41:56AM -0500, Eric Blake wrote:
> On 06/05/2017 10:38 AM, Michael S. Tsirkin wrote:
> > On Mon, Jun 05, 2017 at 04:57:29PM +0800, Wei Wang wrote:
> >> This patch enables the virtio-net tx queue size to be configurable
> >> between 256 and 1024 by the user. The queue size specified by the
> >> user should be power of 2. If "tx_queue_size" is not offered by the
> >> user, the default queue size, 1024, will be used.
> >>
> 
> >> +    if (n->net_conf.tx_queue_size < VIRTIO_NET_TX_QUEUE_MIN_SIZE ||
> >> +        n->net_conf.tx_queue_size > VIRTQUEUE_MAX_SIZE ||
> >> +        (n->net_conf.tx_queue_size & (n->net_conf.tx_queue_size - 1))) {
> > 
> > Pls use is_power_of_2.
> > 
> >> +        error_setg(errp, "Invalid tx_queue_size (= %" PRIu16 "), "
> >> +                   "must be a power of 2 between %d and %d.",
> 
> No trailing '.' in error_setg() messages, please.
> 
> >> +                   n->net_conf.tx_queue_size, 
> >> VIRTIO_NET_TX_QUEUE_MIN_SIZE,
> >> +                   VIRTQUEUE_MAX_SIZE);
> > 
> > I think management will need a way to discover the limits for
> > this value. Not sure how. Cc QAPI maintainers.
> 
> Is this something that can be documented? Or is it a runtime-variable
> limit, where you will need to query the limit on a per-machine basis?
> Given that it looks like compile-time documentation, I'm leaning towards
> documentation being sufficient.

We are likely to change the limits with time. E.g.
VIRTIO_NET_TX_QUEUE_MIN_SIZE is arbitrary.

> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org
>