On Wed, Mar 06, 2013 at 04:22:09PM +1100, Rusty Russell wrote:
> We use inline and get gcc to do the right thing inlining the
> "indirect" traversal functions. This also means we don't need to
> clean the sgs.
>
> for i in `seq 50`; do /usr/bin/time -f 'Wall time:%e' ./vringh_test --indirect --eventidx --parallel --fast-vringh; done 2>&1 | stats --trim-outliers:
>
> Before:
> Using CPUS 0 and 3
> Guest: notified 0, pinged 39014-39063(39062)
> Host: notified 39014-39063(39062), pinged 0
> Wall time:1.900000-2.350000(1.921875)
>
> After:
> Using CPUS 0 and 3
> Guest: notified 0, pinged 39062-39063(39063)
> Host: notified 39062-39063(39063), pinged 0
> Wall time:1.760000-2.220000(1.789167)
>
> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
It's pretty cool that gcc is able to optimize it like this.
Which gcc version did you use here?
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c537385..a78ad45 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -98,13 +98,31 @@ struct vring_virtqueue
>
> #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
>
> +static inline struct scatterlist *sg_next_chained(struct scatterlist *sg,
> + unsigned int *count)
> +{
> + return sg_next(sg);
> +}
> +
> +static inline struct scatterlist *sg_next_arr(struct scatterlist *sg,
> + unsigned int *count)
> +{
> + if (--(*count) == 0)
> + return NULL;
> + return sg + 1;
> +}
> +
> /* Set up an indirect table of descriptors and add it to the queue. */
> -static int vring_add_indirect(struct vring_virtqueue *vq,
> - struct scatterlist *sgs[],
> - unsigned int total_sg,
> - unsigned int out_sgs,
> - unsigned int in_sgs,
> - gfp_t gfp)
> +static inline int vring_add_indirect(struct vring_virtqueue *vq,
> + struct scatterlist *sgs[],
> + struct scatterlist *(*next)
> + (struct scatterlist *, unsigned int *),
> + unsigned int total_sg,
> + unsigned int total_out,
> + unsigned int total_in,
> + unsigned int out_sgs,
> + unsigned int in_sgs,
> + gfp_t gfp)
> {
> struct vring_desc *desc;
> unsigned head;
> @@ -125,7 +143,7 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
> /* 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)) {
> + for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
> desc[i].flags = VRING_DESC_F_NEXT;
> desc[i].addr = sg_phys(sg);
> desc[i].len = sg->length;
> @@ -134,7 +152,7 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
> }
> }
> for (; n < (out_sgs + in_sgs); n++) {
> - for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
> desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
> desc[i].addr = sg_phys(sg);
> desc[i].len = sg->length;
> @@ -163,17 +181,20 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
> return head;
> }
>
> -static int virtqueue_add(struct virtqueue *_vq,
> - struct scatterlist *sgs[],
> - unsigned int total_sg,
> - unsigned int out_sgs,
> - unsigned int in_sgs,
> - void *data,
> - gfp_t gfp)
> +static inline int virtqueue_add(struct virtqueue *_vq,
> + struct scatterlist *sgs[],
> + struct scatterlist *(*next)
> + (struct scatterlist *, unsigned int *),
> + unsigned int total_out,
> + unsigned int total_in,
> + unsigned int out_sgs,
> + unsigned int in_sgs,
> + void *data,
> + gfp_t gfp)
> {
> struct vring_virtqueue *vq = to_vvq(_vq);
> struct scatterlist *sg;
> - unsigned int i, n, avail, uninitialized_var(prev);
> + unsigned int i, n, avail, uninitialized_var(prev), total_sg;
> int head;
>
> START_USE(vq);
> @@ -193,11 +214,14 @@ static int virtqueue_add(struct virtqueue *_vq,
> }
> #endif
>
> + total_sg = total_in + total_out;
> +
> /* If the host supports indirect descriptor tables, and we have multiple
> * buffers, then go indirect. FIXME: tune this threshold */
> if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
> - head = vring_add_indirect(vq, sgs, total_sg, out_sgs, in_sgs,
> - gfp);
> + head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
> + total_in,
> + out_sgs, in_sgs, gfp);
> if (likely(head >= 0))
> goto add_head;
> }
> @@ -222,7 +246,7 @@ static int virtqueue_add(struct virtqueue *_vq,
>
> head = i = vq->free_head;
> for (n = 0; n < out_sgs; n++) {
> - for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + for (sg = sgs[n]; sg; sg = next(sg, &total_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;
> @@ -231,7 +255,7 @@ static int virtqueue_add(struct virtqueue *_vq,
> }
> }
> for (; n < (out_sgs + in_sgs); n++) {
> - for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> + for (sg = sgs[n]; sg; sg = next(sg, &total_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;
> @@ -293,21 +317,12 @@ int virtqueue_add_buf(struct virtqueue *_vq,
> 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(_vq, sgs, out+in, out ? 1 : 0, in ? 1 : 0,
> - data, gfp);
> + return virtqueue_add(_vq, sgs, sg_next_arr,
> + out, in, out ? 1 : 0, in ? 1 : 0, data, gfp);
> }
> EXPORT_SYMBOL_GPL(virtqueue_add_buf);
>
> @@ -332,15 +347,21 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
> void *data,
> gfp_t gfp)
> {
> - unsigned int i, total_sg;
> + unsigned int i, total_out, total_in;
>
> /* Count them first. */
> - for (i = total_sg = 0; i < out_sgs + in_sgs; i++) {
> + for (i = total_out = total_in = 0; i < out_sgs; i++) {
> + struct scatterlist *sg;
> + for (sg = sgs[i]; sg; sg = sg_next(sg))
> + total_out++;
> + }
> + for (; i < out_sgs + in_sgs; i++) {
> struct scatterlist *sg;
> for (sg = sgs[i]; sg; sg = sg_next(sg))
> - total_sg++;
> + total_in++;
> }
> - return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs, data, gfp);
> + return virtqueue_add(_vq, sgs, sg_next_chained,
> + total_out, total_in, out_sgs, in_sgs, data, gfp);
> }
> EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
>
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