The following patch allows us to improve Windows virtio block driver performance on small size requests. Additionally, it leads to reducing of cpu usage on write IOs
repository: /home/vadimr/work/win7/qemu branch: master commit 68290c4e9c96f345d544ca5d2b89f27a1e67e27a Author: Vadim Rozenfeld <vad...@localhost.localdomain> Date: Mon Jan 11 09:00:21 2010 +0200 [RFC][PATCH] small IOs performance for windows guests, running on top of virtio block device diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c index a2f0639..0e3a8d5 100644 --- a/hw/virtio-blk.c +++ b/hw/virtio-blk.c @@ -28,6 +28,7 @@ typedef struct VirtIOBlock char serial_str[BLOCK_SERIAL_STRLEN + 1]; QEMUBH *bh; size_t config_size; + unsigned int pending; } VirtIOBlock; static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev) @@ -87,6 +88,8 @@ typedef struct VirtIOBlockReq struct VirtIOBlockReq *next; } VirtIOBlockReq; +static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq); + static void virtio_blk_req_complete(VirtIOBlockReq *req, int status) { VirtIOBlock *s = req->dev; @@ -95,6 +98,11 @@ static void virtio_blk_req_complete(VirtIOBlockReq *req, int status) virtqueue_push(s->vq, &req->elem, req->qiov.size + sizeof(*req->in)); virtio_notify(&s->vdev, s->vq); + if(--s->pending == 0) { + virtio_queue_set_notification(s->vq, 1); + virtio_blk_handle_output(&s->vdev, s->vq); + } + qemu_free(req); } @@ -340,6 +348,9 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq) exit(1); } + if(++s->pending == 1) + virtio_queue_set_notification(s->vq, 0); + req->out = (void *)req->elem.out_sg[0].iov_base; req->in = (void *)req->elem.in_sg[req->elem.in_num - 1].iov_base;