Skip to content

Commit

Permalink
virtio_ring: assume sgs are always well-formed.
Browse files Browse the repository at this point in the history 
We used to have several callers which just used arrays.  They're
gone, so we can use sg_next() everywhere, simplifying the code.

On my laptop, this slowed down vring_bench by 15%:

vring_bench before:
	936153354-967745359(9.44739e+08+/-6.1e+06)ns
vring_bench after:
	1061485790-1104800648(1.08254e+09+/-6.6e+06)ns

However, a more realistic test using pktgen on a AMD FX(tm)-8320 saw
a few percent improvement:

pktgen before:
  767390-792966(785159+/-6.5e+03)pps 356-367(363.75+/-2.9)Mb/sec (356068960-367936224(3.64314e+08+/-3e+06)bps) errors: 0

pktgen after:
   787781-796334(793165+/-2.4e+03)pps 365-369(367.5+/-1.2)Mb/sec (365530384-369498976(3.68028e+08+/-1.1e+06)bps) errors: 0

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
  • Loading branch information
Rusty Russell authored and David S. Miller committed Sep 13, 2014
1 parent a583544 commit eeebf9b
Showing 1 changed file with 19 additions and 49 deletions.
68 changes: 19 additions & 49 deletions drivers/virtio/virtio_ring.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -99,28 +99,10 @@ 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 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)
Expand All @@ -144,7 +126,7 @@ static inline 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 = next(sg, &total_out)) {
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;
Expand All @@ -153,7 +135,7 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
}
}
for (; n < (out_sgs + in_sgs); n++) {
for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
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;
Expand Down Expand Up @@ -186,18 +168,15 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,

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 total_sg,
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), total_sg;
unsigned int i, n, avail, uninitialized_var(prev);
int head;

START_USE(vq);
Expand All @@ -222,13 +201,10 @@ static inline 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, next, total_sg, total_out,
total_in,
head = vring_add_indirect(vq, sgs, total_sg,
out_sgs, in_sgs, gfp);
if (likely(head >= 0))
goto add_head;
Expand All @@ -254,7 +230,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,

head = i = vq->free_head;
for (n = 0; n < out_sgs; n++) {
for (sg = sgs[n]; sg; sg = next(sg, &total_out)) {
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;
Expand All @@ -263,7 +239,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
}
}
for (; n < (out_sgs + in_sgs); n++) {
for (sg = sgs[n]; sg; sg = next(sg, &total_in)) {
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;
Expand Down Expand Up @@ -324,29 +300,23 @@ int virtqueue_add_sgs(struct virtqueue *_vq,
void *data,
gfp_t gfp)
{
unsigned int i, total_out, total_in;
unsigned int i, total_sg = 0;

/* Count them first. */
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++) {
for (i = 0; i < out_sgs + in_sgs; i++) {
struct scatterlist *sg;
for (sg = sgs[i]; sg; sg = sg_next(sg))
total_in++;
total_sg++;
}
return virtqueue_add(_vq, sgs, sg_next_chained,
total_out, total_in, out_sgs, in_sgs, data, gfp);
return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_sgs);

/**
* virtqueue_add_outbuf - expose output buffers to other end
* @vq: the struct virtqueue we're talking about.
* @sgs: array of scatterlists (need not be terminated!)
* @num: the number of scatterlists readable by other side
* @sg: scatterlist (must be well-formed and terminated!)
* @num: the number of entries in @sg readable by other side
* @data: the token identifying the buffer.
* @gfp: how to do memory allocations (if necessary).
*
Expand All @@ -356,19 +326,19 @@ EXPORT_SYMBOL_GPL(virtqueue_add_sgs);
* Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
*/
int virtqueue_add_outbuf(struct virtqueue *vq,
struct scatterlist sg[], unsigned int num,
struct scatterlist *sg, unsigned int num,
void *data,
gfp_t gfp)
{
return virtqueue_add(vq, &sg, sg_next_arr, num, 0, 1, 0, data, gfp);
return virtqueue_add(vq, &sg, num, 1, 0, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);

/**
* virtqueue_add_inbuf - expose input buffers to other end
* @vq: the struct virtqueue we're talking about.
* @sgs: array of scatterlists (need not be terminated!)
* @num: the number of scatterlists writable by other side
* @sg: scatterlist (must be well-formed and terminated!)
* @num: the number of entries in @sg writable by other side
* @data: the token identifying the buffer.
* @gfp: how to do memory allocations (if necessary).
*
Expand All @@ -378,11 +348,11 @@ EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);
* Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
*/
int virtqueue_add_inbuf(struct virtqueue *vq,
struct scatterlist sg[], unsigned int num,
struct scatterlist *sg, unsigned int num,
void *data,
gfp_t gfp)
{
return virtqueue_add(vq, &sg, sg_next_arr, 0, num, 0, 1, data, gfp);
return virtqueue_add(vq, &sg, num, 0, 1, data, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);

Expand Down

0 comments on commit eeebf9b

Please sign in to comment.