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From: "Ouyang, Changchun" <changchun.ouyang@intel.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Thread-Topic: [PATCH v2 1/2] virtio: fix queue size and number of descriptors
Thread-Index: AQHQwxujRXtWyx73F0mgqHbCMM9uUZ3lXqow
Date: Tue, 21 Jul 2015 05:06:03 +0000
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Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v2 1/2] virtio: fix queue size and number of
descriptors
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> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Tuesday, July 21, 2015 2:41 AM
> To: Ouyang, Changchun
> Cc: dev@dpdk.org; Stephen Hemminger
> Subject: [PATCH v2 1/2] virtio: fix queue size and number of descriptors
>=20
> The virtual queue ring size and the number of slots actually usable are
> separate parameters. In the most common environment (QEMU) the virtual
> queue ring size is 256, but some environments the ring maybe much larger.
>=20
> The ring size comes from the host and the driver must use the actual size
> passed.
>=20
> The number of descriptors can be either zero to use the whole available r=
ing,
> or some value smaller. This is used to limit the number of mbufs allocate=
d for
> the receive ring. If more descriptors are requested than available the si=
ze is
> silently truncated.
>=20
> Note: the ring size (from host) must be a power of two, but the number of
> descriptors used can be any size from 1 to the size of the virtual ring.
>=20
> Reported-by: Ouyang Changchun <changchun.ouyang@intel.com>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Basically ok for this change, so
Acked-by: Changchun Ouyang <changchun.ouyang@intel.com>
> ---
> drivers/net/virtio/virtio_ethdev.c | 17 ++++-------------
> 1 file changed, 4 insertions(+), 13 deletions(-)
>=20
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index 9ca9bb2..d460d89 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -276,8 +276,6 @@ int virtio_dev_queue_setup(struct rte_eth_dev *dev,
> */
> vq_size =3D VIRTIO_READ_REG_2(hw, VIRTIO_PCI_QUEUE_NUM);
> PMD_INIT_LOG(DEBUG, "vq_size: %d nb_desc:%d", vq_size,
> nb_desc);
> - if (nb_desc =3D=3D 0)
> - nb_desc =3D vq_size;
> if (vq_size =3D=3D 0) {
> PMD_INIT_LOG(ERR, "%s: virtqueue does not exist",
> __func__);
> return -EINVAL;
> @@ -288,16 +286,6 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
> return -EINVAL;
> }
>=20
> - 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 =3D nb_desc;
> - }
> -
> if (queue_type =3D=3D VTNET_RQ) {
> snprintf(vq_name, sizeof(vq_name), "port%d_rvq%d",
> dev->data->port_id, queue_idx);
> @@ -325,7 +313,10 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
> vq->queue_id =3D queue_idx;
> vq->vq_queue_index =3D vtpci_queue_idx;
> vq->vq_nentries =3D vq_size;
> - vq->vq_free_cnt =3D vq_size;
> +
> + if (nb_desc =3D=3D 0 || nb_desc > vq_size)
> + nb_desc =3D vq_size;
> + vq->vq_free_cnt =3D nb_desc;
>=20
> /*
> * Reserve a memzone for vring elements
> --
> 2.1.4