From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dpdk.org (dpdk.org [92.243.14.124]) by inbox.dpdk.org (Postfix) with ESMTP id 32BD0A2EFC for ; Tue, 17 Sep 2019 07:29:22 +0200 (CEST) Received: from [92.243.14.124] (localhost [127.0.0.1]) by dpdk.org (Postfix) with ESMTP id 33A171BFC7; Tue, 17 Sep 2019 07:29:09 +0200 (CEST) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by dpdk.org (Postfix) with ESMTP id F3B251BF37 for ; Tue, 17 Sep 2019 07:29:06 +0200 (CEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 79F0428; Mon, 16 Sep 2019 22:29:06 -0700 (PDT) Received: from net-arm-thunderx2-01.test.ast.arm.com (net-arm-thunderx2-01.shanghai.arm.com [10.169.40.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A57E73F575; Mon, 16 Sep 2019 22:31:34 -0700 (PDT) From: Joyce Kong To: dev@dpdk.org Cc: nd@arm.com, maxime.coquelin@redhat.com, yinan.wang@intel.com, bruce.richardson@intel.com, tiwei.bie@intel.com, zhihong.wang@intel.com, amorenoz@redhat.com, xiao.w.wang@intel.com, yong.liu@intel.com, jfreimann@redhat.com, honnappa.nagarahalli@arm.com, gavin.hu@arm.com Date: Tue, 17 Sep 2019 13:28:26 +0800 Message-Id: <1568698107-36668-3-git-send-email-joyce.kong@arm.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1568698107-36668-1-git-send-email-joyce.kong@arm.com> References: <1568698107-36668-1-git-send-email-joyce.kong@arm.com> In-Reply-To: <1566893979-3290-1-git-send-email-joyce.kong@arm.com> References: <1566893979-3290-1-git-send-email-joyce.kong@arm.com> Subject: [dpdk-dev] [PATCH v4 2/2] virtio: one way barrier for packed vring desc used flags X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend and backend are assumed to be implemented in software, that is they can run on identical CPUs in an SMP configuration. Thus a weak form of memory barriers like rte_smp_r/wmb, other than rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1) and yields better performance. For the above case, this patch helps yielding even better performance by replacing the two-way barriers with C11 one-way barriers for used flags in packed ring. Signed-off-by: Joyce Kong Reviewed-by: Gavin Hu Reviewed-by: Phil Yang Reviewed-by: Maxime Coquelin --- drivers/net/virtio/virtio_rxtx.c | 12 +++++++--- drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++-- drivers/net/virtio/virtqueue.h | 28 +++++++++++++++++++++++- lib/librte_vhost/virtio_net.c | 5 ++--- 4 files changed, 40 insertions(+), 9 deletions(-) diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c index a87ffe1..2f0879c 100644 --- a/drivers/net/virtio/virtio_rxtx.c +++ b/drivers/net/virtio/virtio_rxtx.c @@ -122,9 +122,11 @@ virtqueue_dequeue_burst_rx_packed(struct virtqueue *vq, for (i = 0; i < num; i++) { used_idx = vq->vq_used_cons_idx; + /* desc_is_used has a load-acquire or rte_cio_rmb inside + * and wait for used desc in virtqueue. + */ if (!desc_is_used(&desc[used_idx], vq)) return i; - virtio_rmb(vq->hw->weak_barriers); len[i] = desc[used_idx].len; id = desc[used_idx].id; cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie; @@ -233,8 +235,10 @@ virtio_xmit_cleanup_inorder_packed(struct virtqueue *vq, int num) struct vq_desc_extra *dxp; used_idx = vq->vq_used_cons_idx; + /* desc_is_used has a load-acquire or rte_cio_rmb inside + * and wait for used desc in virtqueue. + */ while (num > 0 && desc_is_used(&desc[used_idx], vq)) { - virtio_rmb(vq->hw->weak_barriers); id = desc[used_idx].id; do { curr_id = used_idx; @@ -265,8 +269,10 @@ virtio_xmit_cleanup_normal_packed(struct virtqueue *vq, int num) struct vq_desc_extra *dxp; used_idx = vq->vq_used_cons_idx; + /* desc_is_used has a load-acquire or rte_cio_rmb inside + * and wait for used desc in virtqueue. + */ while (num-- && desc_is_used(&desc[used_idx], vq)) { - virtio_rmb(vq->hw->weak_barriers); id = desc[used_idx].id; dxp = &vq->vq_descx[id]; vq->vq_used_cons_idx += dxp->ndescs; diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c b/drivers/net/virtio/virtio_user/virtio_user_dev.c index 7911c39..1c575d0 100644 --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c @@ -698,8 +698,8 @@ virtio_user_handle_cq_packed(struct virtio_user_dev *dev, uint16_t queue_idx) if (vq->used_wrap_counter) flags |= VRING_PACKED_DESC_F_AVAIL_USED; - rte_smp_wmb(); - vring->desc[vq->used_idx].flags = flags; + __atomic_store_n(&vring->desc[vq->used_idx].flags, flags, + __ATOMIC_RELEASE); vq->used_idx += n_descs; if (vq->used_idx >= dev->queue_size) { diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h index b728ff8..8d7f197 100644 --- a/drivers/net/virtio/virtqueue.h +++ b/drivers/net/virtio/virtqueue.h @@ -54,6 +54,32 @@ virtio_wmb(uint8_t weak_barriers) rte_cio_wmb(); } +static inline uint16_t +virtqueue_fetch_flags_packed(struct vring_packed_desc *dp, + uint8_t weak_barriers) +{ + uint16_t flags; + + if (weak_barriers) { +/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports + * a better perf(~1.5%), which comes from the saved branch by the compiler. + * The if and else branch are identical with the smp and cio barriers both + * defined as compiler barriers on x86. + */ +#ifdef RTE_ARCH_X86_64 + flags = dp->flags; + rte_smp_rmb(); +#else + flags = __atomic_load_n(&dp->flags, __ATOMIC_ACQUIRE); +#endif + } else { + flags = dp->flags; + rte_cio_rmb(); + } + + return flags; +} + static inline void virtqueue_store_flags_packed(struct vring_packed_desc *dp, uint16_t flags, uint8_t weak_barriers) @@ -307,7 +333,7 @@ desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq) { uint16_t used, avail, flags; - flags = desc->flags; + flags = virtqueue_fetch_flags_packed(desc, vq->hw->weak_barriers); used = !!(flags & VRING_PACKED_DESC_F_USED); avail = !!(flags & VRING_PACKED_DESC_F_AVAIL); diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index e7463ff..241d467 100644 --- a/lib/librte_vhost/virtio_net.c +++ b/lib/librte_vhost/virtio_net.c @@ -110,8 +110,6 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, used_idx -= vq->size; } - rte_smp_wmb(); - for (i = 0; i < vq->shadow_used_idx; i++) { uint16_t flags; @@ -147,7 +145,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, } } - vq->desc_packed[head_idx].flags = head_flags; + __atomic_store_n(&vq->desc_packed[head_idx].flags, head_flags, + __ATOMIC_RELEASE); vhost_log_cache_used_vring(dev, vq, head_idx * -- 2.7.4