From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754381AbbIJHYH (ORCPT ); Thu, 10 Sep 2015 03:24:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54100 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753024AbbIJHXw (ORCPT ); Thu, 10 Sep 2015 03:23:52 -0400 Date: Thu, 10 Sep 2015 10:23:49 +0300 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: "Xie, Huawei" , virtualization@lists.linux-foundation.org Subject: [PATCH 4/4] virtio: introduce avail cache Message-ID: <1441869802-15847-5-git-send-email-mst@redhat.com> References: <1441869802-15847-1-git-send-email-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1441869802-15847-1-git-send-email-mst@redhat.com> X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This allows skipping avail ring writes when they don't need to change. Good for cache locality. Signed-off-by: Michael S. Tsirkin --- drivers/virtio/virtio_ring.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 096b857..14e7ce9 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -91,6 +91,7 @@ struct vring_virtqueue { bool last_add_time_valid; ktime_t last_add_time; #endif + u16 *avail; /* Tokens for callbacks. */ void *data[]; @@ -236,7 +237,10 @@ static inline int virtqueue_add(struct virtqueue *_vq, /* Put entry in available array (but don't update avail->idx until they * do sync). */ avail = virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) & (vq->vring.num - 1); - vq->vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head); + if (vq->avail[avail] != head) { + vq->avail[avail] = head; + vq->vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head); + } /* Descriptors and available array need to be set before we expose the * new available array entries. */ @@ -724,6 +728,11 @@ struct virtqueue *vring_new_virtqueue(unsigned int index, vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); if (!vq) return NULL; + vq->avail = kzalloc(sizeof (*vq->avail) * num, GFP_KERNEL); + if (!vq->avail) { + kfree(vq); + return NULL; + } vring_init(&vq->vring, num, pages, vring_align); vq->vq.callback = callback; -- MST