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[50.53.65.80]) by mx.google.com with ESMTPSA id ur5sm4467129pac.46.2014.08.25.19.08.40 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Aug 2014 19:08:41 -0700 (PDT) Message-Id: <20140826020839.926714726@networkplumber.org> User-Agent: quilt/0.63-1 Date: Mon, 25 Aug 2014 19:07:48 -0700 From: Stephen Hemminger To: Ouyang Changchun References: <20140826020746.062748014@networkplumber.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=virtio-barrier.patch Cc: dev@dpdk.org Subject: [dpdk-dev] [RFC 02/10] virtio: use weak barriers X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Aug 2014 02:04:46 -0000 The DPDK driver only has to deal with the case of running on PCI and with SMP. In this case, the code can use the weaker barriers instead of using hard (fence) barriers. This will help performance. The rationale is explained in Linux kernel virtio_ring.h. To make it clearer that this is a virtio thing and not some generic barrier, prefix the barrier calls with virtio_. Add missing (and needed) barrier between updating ring data structure and notifying host. Signed-off-by: Stephen Hemminger --- lib/librte_pmd_virtio/virtio_ethdev.c | 2 +- lib/librte_pmd_virtio/virtio_rxtx.c | 8 +++++--- lib/librte_pmd_virtio/virtqueue.h | 19 ++++++++++++++----- 3 files changed, 20 insertions(+), 9 deletions(-) --- a/lib/librte_pmd_virtio/virtio_rxtx.c 2014-08-25 19:00:04.146518448 -0700 +++ b/lib/librte_pmd_virtio/virtio_rxtx.c 2014-08-25 19:00:04.142518425 -0700 @@ -454,7 +454,7 @@ virtio_recv_pkts(void *rx_queue, struct nb_used = VIRTQUEUE_NUSED(rxvq); - rmb(); + virtio_rmb(); num = (uint16_t)(likely(nb_used <= nb_pkts) ? nb_used : nb_pkts); num = (uint16_t)(likely(num <= VIRTIO_MBUF_BURST_SZ) ? num : VIRTIO_MBUF_BURST_SZ); @@ -514,6 +514,7 @@ virtio_recv_pkts(void *rx_queue, struct } if (likely(nb_enqueued)) { + virtio_wmb(); if (unlikely(virtqueue_kick_prepare(rxvq))) { virtqueue_notify(rxvq); PMD_RX_LOG(DEBUG, "Notified\n"); @@ -545,7 +546,7 @@ virtio_recv_mergeable_pkts(void *rx_queu nb_used = VIRTQUEUE_NUSED(rxvq); - rmb(); + virtio_rmb(); if (nb_used == 0) return 0; @@ -694,7 +695,7 @@ virtio_xmit_pkts(void *tx_queue, struct PMD_TX_LOG(DEBUG, "%d packets to xmit", nb_pkts); nb_used = VIRTQUEUE_NUSED(txvq); - rmb(); + virtio_rmb(); num = (uint16_t)(likely(nb_used < VIRTIO_MBUF_BURST_SZ) ? nb_used : VIRTIO_MBUF_BURST_SZ); @@ -729,6 +730,7 @@ virtio_xmit_pkts(void *tx_queue, struct } } vq_update_avail_idx(txvq); + virtio_wmb(); txvq->packets += nb_tx; --- a/lib/librte_pmd_virtio/virtqueue.h 2014-08-25 19:00:04.146518448 -0700 +++ b/lib/librte_pmd_virtio/virtqueue.h 2014-08-25 19:00:04.142518425 -0700 @@ -46,9 +46,18 @@ #include "virtio_ring.h" #include "virtio_logs.h" -#define mb() rte_mb() -#define wmb() rte_wmb() -#define rmb() rte_rmb() +/* + * Per virtio_config.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. + * + * This driver is for virtio_pci on SMP and therefore can assume + * weaker (compiler barriers) + */ +#define virtio_mb() rte_mb() +#define virtio_rmb() rte_compiler_barrier() +#define virtio_wmb() rte_compiler_barrier() #ifdef RTE_PMD_PACKET_PREFETCH #define rte_packet_prefetch(p) rte_prefetch1(p) @@ -226,7 +235,7 @@ virtqueue_full(const struct virtqueue *v static inline void vq_update_avail_idx(struct virtqueue *vq) { - rte_compiler_barrier(); + virtio_rmb(); vq->vq_ring.avail->idx = vq->vq_avail_idx; } @@ -256,7 +265,7 @@ static inline void virtqueue_notify(struct virtqueue *vq) { /* - * Ensure updated avail->idx is visible to host. mb() necessary? + * Ensure updated avail->idx is visible to host. * For virtio on IA, the notificaiton is through io port operation * which is a serialization instruction itself. */ --- a/lib/librte_pmd_virtio/virtio_ethdev.c 2014-08-25 19:00:04.146518448 -0700 +++ b/lib/librte_pmd_virtio/virtio_ethdev.c 2014-08-25 19:00:04.142518425 -0700 @@ -171,7 +171,7 @@ virtio_send_command(struct virtqueue *vq uint32_t idx, desc_idx, used_idx; struct vring_used_elem *uep; - rmb(); + virtio_rmb(); used_idx = (uint32_t)(vq->vq_used_cons_idx & (vq->vq_nentries - 1));