[dpdk-dev] [PATCH] net/virtio: add platform memory ordering feature support

[Michael S. Tsirkin]

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.maximets at 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