From mboxrd@z Thu Jan 1 00:00:00 1970 From: Huawei Xie Subject: [PATCH] virtio: avoid avail ring entry index update if equal Date: Wed, 27 Apr 2016 04:53:58 -0400 Message-ID: <1461747238-124446-1-git-send-email-huawei.xie@intel.com> References: <1461259092-9309-1-git-send-email-huawei.xie@intel.com> Cc: stephen@networkplumber.org, mukawa@igel.co.jp, kevin.traynor@intel.com, jianfeng.tan@intel.com, yuanhan.liu@linux.intel.com, Huawei Xie To: dev@dpdk.org Return-path: Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by dpdk.org (Postfix) with ESMTP id 5C68937B4 for ; Wed, 27 Apr 2016 16:58:47 +0200 (CEST) In-Reply-To: <1461259092-9309-1-git-send-email-huawei.xie@intel.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Avail ring is updated by the frontend and consumed by the backend. There are frequent core to core cache transfers for the avail ring. This optmization avoids avail ring entry index update if the entry already holds the same value. As DPDK virtio PMD implements FIFO free descriptor list (also for performance reason of CACHE), in which descriptors are allocated from the head and freed to the tail, with this patch in most cases avail ring will remain the same, then it would be valid in both caches of frontend and backend. Signed-off-by: Huawei Xie Suggested-by: ms >> Michael S. Tsirkin --- drivers/net/virtio/virtqueue.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h index 4e9239e..8c46a83 100644 --- a/drivers/net/virtio/virtqueue.h +++ b/drivers/net/virtio/virtqueue.h @@ -302,7 +302,8 @@ vq_update_avail_ring(struct virtqueue *vq, uint16_t desc_idx) * descriptor. */ avail_idx = (uint16_t)(vq->vq_avail_idx & (vq->vq_nentries - 1)); - vq->vq_ring.avail->ring[avail_idx] = desc_idx; + if (unlikely(vq->vq_ring.avail->ring[avail_idx] != desc_idx)) + vq->vq_ring.avail->ring[avail_idx] = desc_idx; vq->vq_avail_idx++; } -- 2.4.3