From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC] net/virtio: use real barriers for vDPA Date: Fri, 14 Dec 2018 10:01:43 -0500 Message-ID: <20181214095535-mutt-send-email-mst@kernel.org> References: <20181214123704.20110-1-i.maximets@samsung.com> <20181214075506-mutt-send-email-mst@kernel.org> <31e17b3e-84fa-6e20-bab1-ca7b10e923d8@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: dev@dpdk.org, Maxime Coquelin , Xiao Wang , Tiwei Bie , Zhihong Wang , jfreimann@redhat.com, Jason Wang , xiaolong.ye@intel.com, alejandro.lucero@netronome.com, stable@dpdk.org To: Ilya Maximets Return-path: Content-Disposition: inline In-Reply-To: <31e17b3e-84fa-6e20-bab1-ca7b10e923d8@samsung.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Fri, Dec 14, 2018 at 05:03:43PM +0300, Ilya Maximets wrote: > On 14.12.2018 15:58, Michael S. Tsirkin wrote: > > 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: stable@dpdk.org > >> > >> Signed-off-by: Ilya Maximets > > > > Instead of this vendor specific hack, can you please > > use VIRTIO_F_ORDER_PLATFORM? > > Hmm. Yes. You're probably right. > But VIRTIO_F_ORDER_PLATFORM a.k.a. VIRTIO_F_IO_BARRIER is not implemented > anywhere at the time. This will require changes to the whole stack (vhost, > qemu, virtio drivers) to allow the negotiation. You are changing virtio drivers anyway, don't you? > Moreover, I guess that it's > not offered/correctly treated by the current vDPA HW i.e. it allows to work > with weak barriers (It allowed to do that by the spec, but I don't think that > it's right). The idea is that the device (e.g. vdpa backend) can detect that - platform is weakly ordered - VIRTIO_F_ORDER_PLATFORM is not negotiated and then use a software fallback. Slower but safe. > This vendor specific hack could allow to work right now. > > Actually, I'm not sure if vDPA is usable with current QEMU ? > Does anybody know ? If it's usable, than having a hack could be acceptable > for now. If not, of course, we could drop this and implement virtio native > solution. I think it's only usable on x86 right now. > But yes, I agree that virtio native solution should be done anyway regardless > of having or not having hacks like this. > > Maybe I can split the patch in two: > 1. Add ability to use real barriers. ('weak_barriers' always 'true') > 2. Hack to initialize 'weak_barriers' according to subsystem_device_id. > > The first patch will be needed anyway. The second one could be dropped or > applied and replaced in the future by proper solution with VIRTIO_F_ORDER_PLATFORM. > > Thoughts ? I'd rather not do 2 at all since otherwise we will just get more vendors asking us to special-case their hardware. Exposing a new feature bit is not a lot of work at all. > One more thing I have concerns about is that vDPA offers support for earlier > versions of virtio protocol, which looks strange. I suspect things like BE just don't work. Again x86 is fine. > > > > > >> --- > >> > >> 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. > > Sure. I'm not a fan of hacks too, especially inside kernel. > > > > >> 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. > > Yes. I know. I used rte_cio_* barriers which are dpdk equivalent of dma_* > barriers from kernel. > > > > >> @@ -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 > > > >