On Fri, Dec 14, 2018 at 03:37:04PM +0300, Ilya Maximets wrote:
> SMP barriers are OK for software vhost implementation, but vDPA is a
> DMA capable hardware and we have to use at least DMA barriers to
> ensure the memory ordering.
>
> This patch mimics the kernel virtio-net driver in part of choosing
> barriers we need.
>
> Fixes: a3f8150eac6d ("net/ifcvf: add ifcvf vDPA driver")
> Cc: sta...@dpdk.org
>
> Signed-off-by: Ilya Maximets <i.maxim...@samsung.com>
Instead of this vendor specific hack, can you please
use VIRTIO_F_ORDER_PLATFORM?
> ---
>
> Sending as RFC, because the patch is completely not tested. I heve no
> HW to test the real behaviour. And I actually do not know if the
> subsystem_vendor/device_id's are available at the time and has
> IFCVF_SUBSYS_* values inside the real guest system.
>
> One more thing I want to mention that cross net client Live Migration
> is actually not possible without any support from the guest driver.
> Because migration from the software vhost to vDPA will lead to using
> weaker barriers than required.
>
> The similar change (weak_barriers = false) should be made in the linux
> kernel virtio-net driver.
IMHO no, it should use VIRTIO_F_ORDER_PLATFORM.
> Another dirty solution could be to restrict the vDPA support to x86
> systems only.
>
> drivers/net/virtio/virtio_ethdev.c | 9 +++++++
> drivers/net/virtio/virtio_pci.h | 1 +
> drivers/net/virtio/virtio_rxtx.c | 14 +++++-----
> drivers/net/virtio/virtio_user_ethdev.c | 1 +
> drivers/net/virtio/virtqueue.h | 35 +++++++++++++++++++++----
> 5 files changed, 48 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index cb2b2e0bf..249b536fd 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1448,6 +1448,9 @@ virtio_configure_intr(struct rte_eth_dev *dev)
> return 0;
> }
>
> +#define IFCVF_SUBSYS_VENDOR_ID 0x8086
> +#define IFCVF_SUBSYS_DEVICE_ID 0x001A
> +
> /* reset device and renegotiate features if needed */
> static int
> virtio_init_device(struct rte_eth_dev *eth_dev, uint64_t req_features)
> @@ -1477,6 +1480,12 @@ virtio_init_device(struct rte_eth_dev *eth_dev,
> uint64_t req_features)
> if (!hw->virtio_user_dev) {
> pci_dev = RTE_ETH_DEV_TO_PCI(eth_dev);
> rte_eth_copy_pci_info(eth_dev, pci_dev);
> +
> + if (pci_dev->id.subsystem_vendor_id == IFCVF_SUBSYS_VENDOR_ID &&
> + pci_dev->id.subsystem_device_id == IFCVF_SUBSYS_DEVICE_ID)
> + hw->weak_barriers = 0;
> + else
> + hw->weak_barriers = 1;
> }
>
> /* If host does not support both status and MSI-X then disable LSC */
> diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
> index e961a58ca..1f8e719a9 100644
> --- a/drivers/net/virtio/virtio_pci.h
> +++ b/drivers/net/virtio/virtio_pci.h
> @@ -240,6 +240,7 @@ 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/virtio_user_ethdev.c
> b/drivers/net/virtio/virtio_user_ethdev.c
> index f8791391a..f075774b4 100644
> --- a/drivers/net/virtio/virtio_user_ethdev.c
> +++ b/drivers/net/virtio/virtio_user_ethdev.c
> @@ -434,6 +434,7 @@ virtio_user_eth_dev_alloc(struct rte_vdev_device *vdev)
> hw->use_simple_rx = 0;
> hw->use_inorder_rx = 0;
> hw->use_inorder_tx = 0;
> + hw->weak_barriers = 1;
> hw->virtio_user_dev = dev;
> return eth_dev;
> }
> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index 26518ed98..7bf17d3bf 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();
> +}
> +
> +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)
Note kernel uses dma_ barriers not full barriers.
I don't know whether it applies to dpdk.
> @@ -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
