From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id 4CA0B1B200; Fri, 19 Oct 2018 16:01:10 +0200 (CEST) Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 85C5930001E0; Fri, 19 Oct 2018 14:01:09 +0000 (UTC) Received: from localhost.localdomain (ovpn-112-53.ams2.redhat.com [10.36.112.53]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2BB9361B73; Fri, 19 Oct 2018 14:01:00 +0000 (UTC) From: Maxime Coquelin To: dev@dpdk.org, tiwei.bie@intel.com, zhihong.wang@intel.com, jfreimann@redhat.com Cc: stable@dpdk.org, Maxime Coquelin Date: Fri, 19 Oct 2018 16:00:58 +0200 Message-Id: <20181019140058.4981-1-maxime.coquelin@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Fri, 19 Oct 2018 14:01:09 +0000 (UTC) Subject: [dpdk-stable] [PATCH] vhost: avoid memory barriers when no descriptors dequeued X-BeenThere: stable@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches for DPDK stable branches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Oct 2018 14:01:10 -0000 In both split and packed dequeue paths, flush_shadow_used_ring and vhost_ring_call variants gets called even if not packets have been dequeued, and so no descriptors updates happened. It has an impact on CPU pipeline, as memory barriers are used in these functions. This patch don't call these functions if no descriptors have been dequeued. The performance gain with split ring when dequeue zero-copy is disabled should be null, but should be noticeable with packed ring or dequeue zero-copy enabled. Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring") Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path") Cc: stable@dpdk.org Signed-off-by: Maxime Coquelin --- lib/librte_vhost/virtio_net.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index f8794ee19..48228f16b 100644 --- a/lib/librte_vhost/virtio_net.c +++ b/lib/librte_vhost/virtio_net.c @@ -1359,8 +1359,10 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq, } } - flush_shadow_used_ring_split(dev, vq); - vhost_vring_call_split(dev, vq); + if (likely(vq->shadow_used_idx)) { + flush_shadow_used_ring_split(dev, vq); + vhost_vring_call_split(dev, vq); + } } rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]); @@ -1435,7 +1437,7 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq, } vq->last_avail_idx += i; - if (likely(dev->dequeue_zero_copy == 0)) { + if (likely(dev->dequeue_zero_copy == 0 && i != 0)) { do_data_copy_dequeue(vq); if (unlikely(i < count)) vq->shadow_used_idx = i; @@ -1475,8 +1477,10 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq, } } - flush_shadow_used_ring_packed(dev, vq); - vhost_vring_call_packed(dev, vq); + if (likely(vq->shadow_used_idx)) { + flush_shadow_used_ring_packed(dev, vq); + vhost_vring_call_packed(dev, vq); + } } VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__); @@ -1550,7 +1554,7 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq, } } - if (likely(dev->dequeue_zero_copy == 0)) { + if (likely(dev->dequeue_zero_copy == 0 && i != 0)) { do_data_copy_dequeue(vq); if (unlikely(i < count)) vq->shadow_used_idx = i; -- 2.17.1