On Fri, Dec 14, 2018 at 06:38:12PM +0300, Ilya Maximets wrote:
> VIRTIO_F_ORDER_PLATFORM is required to use proper memory barriers
> in case of HW vhost implementations like vDPA.
>
> DMA barriers (rte_cio_*) are sufficent for that purpose.
>
> Previously known as VIRTIO_F_IO_BARRIER.
>
> Signed-off-by: Ilya Maximets <i.maxim...@samsung.com>
> ---
>
> Based on "[RFC] net/virtio: use real barriers for vDPA".
>
> RFC --> PATCH:
> * Dropped vendor-specific hack to determine if we need real barriers.
> * Added VIRTIO_F_ORDER_PLATFORM feature definition and checking.
>
> Note: Patch to change the name of the feature from VIRTIO_F_IO_BARRIER
> to VIRTIO_F_ORDER_PLATFORM is not merged yet:
>
> https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg04114.html
>
> drivers/net/virtio/virtio_ethdev.c | 2 ++
> drivers/net/virtio/virtio_ethdev.h | 3 ++-
> drivers/net/virtio/virtio_pci.h | 7 ++++++
> drivers/net/virtio/virtio_rxtx.c | 14 ++++++------
> drivers/net/virtio/virtqueue.h | 35 +++++++++++++++++++++++++-----
> 5 files changed, 48 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index cb2b2e0bf..5ae7a9650 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1474,6 +1474,8 @@ virtio_init_device(struct rte_eth_dev *eth_dev,
> uint64_t req_features)
> if (virtio_negotiate_features(hw, req_features) < 0)
> return -1;
>
> + hw->weak_barriers = !vtpci_with_feature(hw, VIRTIO_F_ORDER_PLATFORM);
> +
> if (!hw->virtio_user_dev) {
> pci_dev = RTE_ETH_DEV_TO_PCI(eth_dev);
> rte_eth_copy_pci_info(eth_dev, pci_dev);
> diff --git a/drivers/net/virtio/virtio_ethdev.h
> b/drivers/net/virtio/virtio_ethdev.h
> index e0f80e5a4..c098e5ac0 100644
> --- a/drivers/net/virtio/virtio_ethdev.h
> +++ b/drivers/net/virtio/virtio_ethdev.h
> @@ -34,7 +34,8 @@
> 1u << VIRTIO_RING_F_INDIRECT_DESC | \
> 1ULL << VIRTIO_F_VERSION_1 | \
> 1ULL << VIRTIO_F_IN_ORDER | \
> - 1ULL << VIRTIO_F_IOMMU_PLATFORM)
> + 1ULL << VIRTIO_F_IOMMU_PLATFORM | \
> + 1ULL << VIRTIO_F_ORDER_PLATFORM)
>
> #define VIRTIO_PMD_SUPPORTED_GUEST_FEATURES \
> (VIRTIO_PMD_DEFAULT_GUEST_FEATURES | \
> diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
> index e961a58ca..e2f096185 100644
> --- a/drivers/net/virtio/virtio_pci.h
> +++ b/drivers/net/virtio/virtio_pci.h
> @@ -128,6 +128,12 @@ struct virtnet_ctl;
> */
> #define VIRTIO_F_IN_ORDER 35
>
> +/*
> + * This feature indicates that memory accesses by the driver and the device
> + * are ordered in a way described by the platform.
> + */
> +#define VIRTIO_F_ORDER_PLATFORM 36
> +
> /* The Guest publishes the used index for which it expects an interrupt
> * at the end of the avail ring. Host should ignore the avail->flags field.
> */
> /* The Host publishes the avail index for which it expects a kick
> @@ -240,6 +246,7 @@ struct virtio_hw {
> uint8_t use_simple_rx;
> uint8_t use_inorder_rx;
> uint8_t use_inorder_tx;
> + uint8_t weak_barriers;
> bool has_tx_offload;
> bool has_rx_offload;
> uint16_t port_id;
> diff --git a/drivers/net/virtio/virtio_rxtx.c
> b/drivers/net/virtio/virtio_rxtx.c
> index cb8f89f18..66195bf47 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -906,7 +906,7 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf
> **rx_pkts, uint16_t nb_pkts)
>
> nb_used = VIRTQUEUE_NUSED(vq);
>
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
>
> num = likely(nb_used <= nb_pkts) ? nb_used : nb_pkts;
> if (unlikely(num > VIRTIO_MBUF_BURST_SZ))
> @@ -1017,7 +1017,7 @@ virtio_recv_mergeable_pkts_inorder(void *rx_queue,
> nb_used = RTE_MIN(nb_used, nb_pkts);
> nb_used = RTE_MIN(nb_used, VIRTIO_MBUF_BURST_SZ);
>
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
>
> PMD_RX_LOG(DEBUG, "used:%d", nb_used);
>
> @@ -1202,7 +1202,7 @@ virtio_recv_mergeable_pkts(void *rx_queue,
>
> nb_used = VIRTQUEUE_NUSED(vq);
>
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
>
> PMD_RX_LOG(DEBUG, "used:%d", nb_used);
>
> @@ -1365,7 +1365,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
> PMD_TX_LOG(DEBUG, "%d packets to xmit", nb_pkts);
> nb_used = VIRTQUEUE_NUSED(vq);
>
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
> if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
> virtio_xmit_cleanup(vq, nb_used);
>
> @@ -1407,7 +1407,7 @@ virtio_xmit_pkts(void *tx_queue, struct rte_mbuf
> **tx_pkts, uint16_t nb_pkts)
> /* Positive value indicates it need free vring descriptors */
> if (unlikely(need > 0)) {
> nb_used = VIRTQUEUE_NUSED(vq);
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
> need = RTE_MIN(need, (int)nb_used);
>
> virtio_xmit_cleanup(vq, need);
> @@ -1463,7 +1463,7 @@ virtio_xmit_pkts_inorder(void *tx_queue,
> PMD_TX_LOG(DEBUG, "%d packets to xmit", nb_pkts);
> nb_used = VIRTQUEUE_NUSED(vq);
>
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
> if (likely(nb_used > vq->vq_nentries - vq->vq_free_thresh))
> virtio_xmit_cleanup_inorder(vq, nb_used);
>
> @@ -1511,7 +1511,7 @@ virtio_xmit_pkts_inorder(void *tx_queue,
> need = slots - vq->vq_free_cnt;
> if (unlikely(need > 0)) {
> nb_used = VIRTQUEUE_NUSED(vq);
> - virtio_rmb();
> + virtio_rmb(hw->weak_barriers);
> need = RTE_MIN(need, (int)nb_used);
>
> virtio_xmit_cleanup_inorder(vq, need);
> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index 26518ed98..6b9055a1f 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -19,15 +19,40 @@
> struct rte_mbuf;
>
> /*
> - * Per virtio_config.h in Linux.
> + * Per virtio_ring.h in Linux.
> * For virtio_pci on SMP, we don't need to order with respect to MMIO
> * accesses through relaxed memory I/O windows, so smp_mb() et al are
> * sufficient.
> *
> + * For using virtio to talk to real devices (eg. vDPA) we do need real
> + * barriers.
> */
> -#define virtio_mb() rte_smp_mb()
> -#define virtio_rmb() rte_smp_rmb()
> -#define virtio_wmb() rte_smp_wmb()
> +static inline void
> +virtio_mb(uint8_t weak_barriers)
> +{
> + if (weak_barriers)
> + rte_smp_mb();
> + else
> + rte_mb();
> +}
> +
Why doesn't rte_cio_rmb exit?
> +static inline void
> +virtio_rmb(uint8_t weak_barriers)
> +{
> + if (weak_barriers)
> + rte_smp_rmb();
> + else
> + rte_cio_rmb();
> +}
> +
> +static inline void
> +virtio_wmb(uint8_t weak_barriers)
> +{
> + if (weak_barriers)
> + rte_smp_wmb();
> + else
> + rte_cio_wmb();
> +}
>
> #ifdef RTE_PMD_PACKET_PREFETCH
> #define rte_packet_prefetch(p) rte_prefetch1(p)
> @@ -312,7 +337,7 @@ void vq_ring_free_inorder(struct virtqueue *vq, uint16_t
> desc_idx,
> static inline void
> vq_update_avail_idx(struct virtqueue *vq)
> {
> - virtio_wmb();
> + virtio_wmb(vq->hw->weak_barriers);
> vq->vq_ring.avail->idx = vq->vq_avail_idx;
> }
>
> --
> 2.17.1
