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Message-ID: <512342A9.9070203@cn.fujitsu.com>
Date: Tue, 19 Feb 2013 17:15:21 +0800
From: Wanlong Gao <gaowanlong@...fujitsu.com>
To: Rusty Russell <rusty@...tcorp.com.au>
CC: Paolo Bonzini <pbonzini@...hat.com>,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 02/16] virtio_ring: virtqueue_add_sgs, to add multiple
sgs.
On 02/19/2013 03:56 PM, Rusty Russell wrote:
> virtio_scsi can really use this, to avoid the current hack of copying
> the whole sg array. Some other things get slightly neater, too.
>
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
I like this simple implementation.
Reviewed-by: Wanlong Gao <gaowanlong@...fujitsu.com>
> ---
> drivers/virtio/virtio_ring.c | 144 ++++++++++++++++++++++++++++++------------
> include/linux/virtio.h | 7 ++
> 2 files changed, 109 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 245177c..27e31d3 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -100,14 +100,16 @@ struct vring_virtqueue
>
> /* Set up an indirect table of descriptors and add it to the queue. */
> static int vring_add_indirect(struct vring_virtqueue *vq,
> - struct scatterlist sg[],
> - unsigned int out,
> - unsigned int in,
> + struct scatterlist *sgs[],
> + unsigned int total_sg,
> + unsigned int out_sgs,
> + unsigned int in_sgs,
> gfp_t gfp)
> {
> struct vring_desc *desc;
> unsigned head;
> - int i;
> + struct scatterlist *sg;
> + int i, n;
>
> /*
> * We require lowmem mappings for the descriptors because
> @@ -116,25 +118,31 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
> */
> gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
>
> - desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
> + desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
> if (!desc)
> return -ENOMEM;
>
> - /* Transfer entries from the sg list into the indirect page */
> - for (i = 0; i < out; i++) {
> - desc[i].flags = VRING_DESC_F_NEXT;
> - desc[i].addr = sg_phys(sg);
> - desc[i].len = sg->length;
> - desc[i].next = i+1;
> - sg++;
> + /* Transfer entries from the sg lists into the indirect page */
> + i = 0;
> + for (n = 0; n < out_sgs; n++) {
> + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + desc[i].flags = VRING_DESC_F_NEXT;
> + desc[i].addr = sg_phys(sg);
> + desc[i].len = sg->length;
> + desc[i].next = i+1;
> + i++;
> + }
> }
> - for (; i < (out + in); i++) {
> - desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> - desc[i].addr = sg_phys(sg);
> - desc[i].len = sg->length;
> - desc[i].next = i+1;
> - sg++;
> + for (; n < (out_sgs + in_sgs); n++) {
> + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> + desc[i].addr = sg_phys(sg);
> + desc[i].len = sg->length;
> + desc[i].next = i+1;
> + i++;
> + }
> }
> + BUG_ON(i != total_sg);
>
> /* Last one doesn't continue. */
> desc[i-1].flags &= ~VRING_DESC_F_NEXT;
> @@ -176,8 +184,48 @@ int virtqueue_add_buf(struct virtqueue *_vq,
> void *data,
> gfp_t gfp)
> {
> + struct scatterlist *sgs[2];
> + unsigned int i;
> +
> + sgs[0] = sg;
> + sgs[1] = sg + out;
> +
> + /* Workaround until callers pass well-formed sgs. */
> + for (i = 0; i < out + in; i++)
> + sg_unmark_end(sg + i);
> +
> + sg_mark_end(sg + out + in - 1);
> + if (out && in)
> + sg_mark_end(sg + out - 1);
> +
> + return virtqueue_add_sgs(_vq, sgs, out ? 1 : 0, in ? 1 : 0, data, gfp);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_add_buf);
> +
> +/**
> + * virtqueue_add_sgs - expose buffers to other end
> + * @vq: the struct virtqueue we're talking about.
> + * @sgs: array of terminated scatterlists.
> + * @out_num: the number of scatterlists readable by other side
> + * @in_num: the number of scatterlists which are writable (after readable ones)
> + * @data: the token identifying the buffer.
> + * @gfp: how to do memory allocations (if necessary).
> + *
> + * Caller must ensure we don't call this with other virtqueue operations
> + * at the same time (except where noted).
> + *
> + * Returns zero or a negative error (ie. ENOSPC, ENOMEM).
> + */
> +int virtqueue_add_sgs(struct virtqueue *_vq,
> + struct scatterlist *sgs[],
> + unsigned int out_sgs,
> + unsigned int in_sgs,
> + void *data,
> + gfp_t gfp)
> +{
> struct vring_virtqueue *vq = to_vvq(_vq);
> - unsigned int i, avail, uninitialized_var(prev);
> + struct scatterlist *sg;
> + unsigned int i, n, avail, uninitialized_var(prev), total_sg;
> int head;
>
> START_USE(vq);
> @@ -197,46 +245,58 @@ int virtqueue_add_buf(struct virtqueue *_vq,
> }
> #endif
>
> + /* Count them first. */
> + for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
> + struct scatterlist *sg;
> + for (sg = sgs[i]; sg; sg = sg_next(sg))
> + total_sg++;
> + }
> +
> /* If the host supports indirect descriptor tables, and we have multiple
> * buffers, then go indirect. FIXME: tune this threshold */
> - if (vq->indirect && (out + in) > 1 && vq->vq.num_free) {
> - head = vring_add_indirect(vq, sg, out, in, gfp);
> + if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
> + head = vring_add_indirect(vq, sgs, total_sg, out_sgs, in_sgs,
> + gfp);
> if (likely(head >= 0))
> goto add_head;
> }
>
> - BUG_ON(out + in > vq->vring.num);
> - BUG_ON(out + in == 0);
> + BUG_ON(total_sg > vq->vring.num);
> + BUG_ON(total_sg == 0);
>
> - if (vq->vq.num_free < out + in) {
> + if (vq->vq.num_free < total_sg) {
> pr_debug("Can't add buf len %i - avail = %i\n",
> - out + in, vq->vq.num_free);
> + total_sg, vq->vq.num_free);
> /* FIXME: for historical reasons, we force a notify here if
> * there are outgoing parts to the buffer. Presumably the
> * host should service the ring ASAP. */
> - if (out)
> + if (out_sgs)
> vq->notify(&vq->vq);
> END_USE(vq);
> return -ENOSPC;
> }
>
> /* We're about to use some buffers from the free list. */
> - vq->vq.num_free -= out + in;
> -
> - head = vq->free_head;
> - for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
> - vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
> - vq->vring.desc[i].addr = sg_phys(sg);
> - vq->vring.desc[i].len = sg->length;
> - prev = i;
> - sg++;
> + vq->vq.num_free -= total_sg;
> +
> + head = i = vq->free_head;
> + for (n = 0; n < out_sgs; n++) {
> + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
> + vq->vring.desc[i].addr = sg_phys(sg);
> + vq->vring.desc[i].len = sg->length;
> + prev = i;
> + i = vq->vring.desc[i].next;
> + }
> }
> - for (; in; i = vq->vring.desc[i].next, in--) {
> - vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> - vq->vring.desc[i].addr = sg_phys(sg);
> - vq->vring.desc[i].len = sg->length;
> - prev = i;
> - sg++;
> + for (; n < (out_sgs + in_sgs); n++) {
> + for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> + vq->vring.desc[i].addr = sg_phys(sg);
> + vq->vring.desc[i].len = sg->length;
> + prev = i;
> + i = vq->vring.desc[i].next;
> + }
> }
> /* Last one doesn't continue. */
> vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
> @@ -269,7 +329,7 @@ add_head:
>
> return 0;
> }
> -EXPORT_SYMBOL_GPL(virtqueue_add_buf);
> +EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
>
> /**
> * virtqueue_kick_prepare - first half of split virtqueue_kick call.
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index ff6714e..6eff15b 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -40,6 +40,13 @@ int virtqueue_add_buf(struct virtqueue *vq,
> void *data,
> gfp_t gfp);
>
> +int virtqueue_add_sgs(struct virtqueue *vq,
> + struct scatterlist *sgs[],
> + unsigned int out_sgs,
> + unsigned int in_sgs,
> + void *data,
> + gfp_t gfp);
> +
> void virtqueue_kick(struct virtqueue *vq);
>
> bool virtqueue_kick_prepare(struct virtqueue *vq);
>
--
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