From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38150) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aK3hr-0004Tg-8D for qemu-devel@nongnu.org; Fri, 15 Jan 2016 07:42:20 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aK3hq-0005fP-4r for qemu-devel@nongnu.org; Fri, 15 Jan 2016 07:42:19 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39044) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aK3hp-0005fI-Vg for qemu-devel@nongnu.org; Fri, 15 Jan 2016 07:42:18 -0500 From: Paolo Bonzini Date: Fri, 15 Jan 2016 13:41:58 +0100 Message-Id: <1452861718-25806-11-git-send-email-pbonzini@redhat.com> In-Reply-To: <1452861718-25806-1-git-send-email-pbonzini@redhat.com> References: <1452861718-25806-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PATCH 10/10] virtio: combine write of an entry into used ring List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Vincenzo Maffione , mst@redhat.com From: Vincenzo Maffione Fill in an element of the used ring with a single combined access to the guest physical memory, rather than using two separated accesses. This reduces the overhead due to expensive address translation. Signed-off-by: Vincenzo Maffione Message-Id: Signed-off-by: Paolo Bonzini --- hw/virtio/virtio.c | 25 ++++++++++++------------- 1 file changed, 12 insertions(+), 13 deletions(-) diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 01142da..96bd420 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -153,18 +153,15 @@ static inline uint16_t vring_get_used_event(VirtQueue *vq) return vring_avail_ring(vq, vq->vring.num); } -static inline void vring_used_ring_id(VirtQueue *vq, int i, uint32_t val) +static inline void vring_used_write(VirtQueue *vq, VRingUsedElem *uelem, + int i) { hwaddr pa; - pa = vq->vring.used + offsetof(VRingUsed, ring[i].id); - virtio_stl_phys(vq->vdev, pa, val); -} - -static inline void vring_used_ring_len(VirtQueue *vq, int i, uint32_t val) -{ - hwaddr pa; - pa = vq->vring.used + offsetof(VRingUsed, ring[i].len); - virtio_stl_phys(vq->vdev, pa, val); + virtio_tswap32s(vq->vdev, &uelem->id); + virtio_tswap32s(vq->vdev, &uelem->len); + pa = vq->vring.used + offsetof(VRingUsed, ring[i]); + address_space_write(&address_space_memory, pa, MEMTXATTRS_UNSPECIFIED, + (void *)uelem, sizeof(VRingUsedElem)); } static uint16_t vring_used_idx(VirtQueue *vq) @@ -273,15 +270,17 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem, void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, unsigned int len, unsigned int idx) { + VRingUsedElem uelem; + trace_virtqueue_fill(vq, elem, len, idx); virtqueue_unmap_sg(vq, elem, len); idx = (idx + vq->used_idx) % vq->vring.num; - /* Get a pointer to the next entry in the used ring. */ - vring_used_ring_id(vq, idx, elem->index); - vring_used_ring_len(vq, idx, len); + uelem.id = elem->index; + uelem.len = len; + vring_used_write(vq, &uelem, idx); } void virtqueue_flush(VirtQueue *vq, unsigned int count) -- 2.5.0