From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ilya Maximets Subject: Re: [RFC] net/virtio: use real barriers for vDPA Date: Fri, 14 Dec 2018 17:03:43 +0300 Message-ID: <31e17b3e-84fa-6e20-bab1-ca7b10e923d8@samsung.com> References: <20181214123704.20110-1-i.maximets@samsung.com> <20181214075506-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit 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: "Michael S. Tsirkin" Return-path: Received: from mailout2.w1.samsung.com (mailout2.w1.samsung.com [210.118.77.12]) by dpdk.org (Postfix) with ESMTP id 408771BBF1 for ; Fri, 14 Dec 2018 15:03:50 +0100 (CET) Received: from eucas1p1.samsung.com (unknown [182.198.249.206]) by mailout2.w1.samsung.com (KnoxPortal) with ESMTP id 20181214140350euoutp020bb8f19231ed1f2b8c8fc5c3b2a40f54~wN-yTpzYg0447104471euoutp02F for ; Fri, 14 Dec 2018 14:03:50 +0000 (GMT) In-Reply-To: <20181214075506-mutt-send-email-mst@kernel.org> Content-Language: en-GB 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 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. 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). 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. 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 ? One more thing I have concerns about is that vDPA offers support for earlier versions of virtio protocol, which looks strange. > > >> --- >> >> 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 > >