Re: [PATCH 4/5] virtio: fix ring size negotiation

["Ouyang, Changchun" <changchun.ouyang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

From: Stephen Hemminger [mailto:stephen@networkplumber.org]
Sent: Thursday, April 16, 2015 1:48 PM
To: Ouyang, Changchun
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 4/5] virtio: fix ring size negotiation

No warning is needed, it just works.

I know it works, but the upper user don’t know the descriptor number is reduced.
I concern it is not so user-friendly here.


On Wed, Apr 15, 2015 at 8:39 PM, Ouyang, Changchun <changchun.ouyang@intel.com<mailto:changchun.ouyang@intel.com>> wrote:


> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org<mailto:dev-bounces@dpdk.org>] On Behalf Of Stephen
> Hemminger
> Sent: Wednesday, April 15, 2015 11:20 PM
> To: dev@dpdk.org<mailto:dev@dpdk.org>
> Subject: [dpdk-dev] [PATCH 4/5] virtio: fix ring size negotiation
>
> This fixes another of the issues with running virtio on non-KVM
> envirionments. For example, Google Compute Engine reports a ring size of
> 16K.
>
> If guest virtio requests more slots than available then the queue should just

I suspect 'more' here should be 'less'?

> be initialized to the smaller value.
>
> Conversely, if the number of descriptors requested exceeds the virtio host
> queue size, then just silently use the smaller host size.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org<mailto:stephen@networkplumber.org>>
> ---
>  lib/librte_pmd_virtio/virtio_ethdev.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/lib/librte_pmd_virtio/virtio_ethdev.c
> b/lib/librte_pmd_virtio/virtio_ethdev.c
> index 3cb9c6a..db0232e 100644
> --- a/lib/librte_pmd_virtio/virtio_ethdev.c
> +++ b/lib/librte_pmd_virtio/virtio_ethdev.c
> @@ -267,13 +267,21 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
>       if (vq_size == 0) {
>               PMD_INIT_LOG(ERR, "%s: virtqueue does not exist",
> __func__);
>               return -EINVAL;
> -     } else if (!rte_is_power_of_2(vq_size)) {
> +     }
> +
> +     if (!rte_is_power_of_2(vq_size)) {
>               PMD_INIT_LOG(ERR, "%s: virtqueue size is not powerof 2",
> __func__);
>               return -EINVAL;
> -     } else if (nb_desc != vq_size) {
> -             PMD_INIT_LOG(ERR, "Warning: nb_desc(%d) is not equal to
> vq size (%d), fall to vq size",
> -                     nb_desc, vq_size);
> -             nb_desc = vq_size;
> +     }
> +
> +     if (nb_desc < vq_size) {
> +             if (!rte_is_power_of_2(nb_desc)) {
> +                     PMD_INIT_LOG(ERR,
> +                                  "nb_desc(%u) size is not powerof 2",
> +                                  nb_desc);
> +                     return -EINVAL;
> +             }
> +             vq_size = nb_desc;
Don't we need a warning when nb_desc > vq_size?

>       }
>
>       if (queue_type == VTNET_RQ) {
> --
> 2.1.4