[PATCH 1/3] virtio_net: pass well-formed sgs to virtqueue_add

Discussion:

[PATCH 1/3] virtio_net: pass well-formed sgs to virtqueue_add_*()

Rusty Russell

2014-09-03 04:29:14 UTC

This is the only driver which doesn't hand virtqueue_add_inbuf and
virtqueue_add_outbuf a well-formed, well-terminated sg. Fix it,
so we can make virtio_add_* simpler.

pktgen results:
modprobe pktgen
echo 'add_device eth0' > /proc/net/pktgen/kpktgend_0
echo nowait 1 > /proc/net/pktgen/eth0
echo count 1000000 > /proc/net/pktgen/eth0
echo clone_skb 100000 > /proc/net/pktgen/eth0
echo dst_mac 4e:14:25:a9:30:ac > /proc/net/pktgen/eth0
echo dst 192.168.1.2 > /proc/net/pktgen/eth0
for i in `seq 20`; do echo start > /proc/net/pktgen/pgctrl; tail -n1 /proc/net/pktgen/eth0; done

Before:
746547-793084(786421+/-9.6e+03)pps 346-367(364.4+/-4.4)Mb/sec (346397808-367990976(3.649e+08+/-4.5e+06)bps) errors: 0

After:
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

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
---
drivers/net/virtio_net.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 59caa06f34a6..31cac511b3c3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -546,8 +546,8 @@ static int add_recvbuf_small(struct receive_queue *rq, gfp_t gfp)
skb_put(skb, GOOD_PACKET_LEN);

hdr = skb_vnet_hdr(skb);
+ sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
-
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);

err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
@@ -563,6 +563,8 @@ static int add_recvbuf_big(struct receive_queue *rq, gfp_t gfp)
char *p;
int i, err, offset;

+ sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
+
/* page in rq->sg[MAX_SKB_FRAGS + 1] is list tail */
for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
first = get_a_page(rq, gfp);
@@ -899,6 +901,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
if (vi->mergeable_rx_bufs)
hdr->mhdr.num_buffers = 0;

+ sg_init_table(sq->sg, MAX_SKB_FRAGS + 2);
if (can_push) {
__skb_push(skb, hdr_len);
num_sg = skb_to_sgvec(skb, sq->sg, 0, skb->len);

--
1.9.1

Rusty Russell

2014-09-03 04:29:16 UTC

Permalink

virtqueue_add() populates the virtqueue descriptor table from the sgs
given. If it uses an indirect descriptor table, then it puts a single
descriptor in the descriptor table pointing to the kmalloc'ed indirect
table where the sg is populated.

Previously vring_add_indirect() did the allocation and the simple
linear layout. We replace that with alloc_indirect() which allocates
the indirect table then chains it like the normal descriptor table so
we can reuse the core logic.

This slows down pktgen by less than 1/2 a percent (which uses direct
descriptors), as well as vring_bench, but it's far neater.

vring_bench before:
1061485790-1104800648(1.08254e+09+/-6.6e+06)ns
vring_bench after:
1125610268-1183528965(1.14172e+09+/-8e+06)ns

pktgen before:
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

pktgen after:
779988-790404(786391+/-2.5e+03)pps 361-366(364.35+/-1.3)Mb/sec (361914432-366747456(3.64885e+08+/-1.2e+06)bps) errors: 0

Now, if we make force indirect descriptors by turning off any_header_sg
in virtio_net.c:

pktgen before:
713773-721062(718374+/-2.1e+03)pps 331-334(332.95+/-0.92)Mb/sec (331190672-334572768(3.33325e+08+/-9.6e+05)bps) errors: 0
pktgen after:
710542-719195(714898+/-2.4e+03)pps 329-333(331.15+/-1.1)Mb/sec (329691488-333706480(3.31713e+08+/-1.1e+06)bps) errors: 0

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
---
drivers/virtio/virtio_ring.c | 125 +++++++++++++++++--------------------------
1 file changed, 50 insertions(+), 75 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 374399c62080..a4ebbffac141 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -99,18 +99,10 @@ struct vring_virtqueue

#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

-/* 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[],
- unsigned int total_sg,
- unsigned int out_sgs,
- unsigned int in_sgs,
- gfp_t gfp)
+static struct vring_desc *alloc_indirect(unsigned int total_sg, gfp_t gfp)
{
- struct vring_desc *desc;
- unsigned head;
- struct scatterlist *sg;
- int i, n;
+ struct vring_desc *desc;
+ unsigned int i;

/*
* We require lowmem mappings for the descriptors because
@@ -119,51 +111,13 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
*/
gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);

- desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
- if (!desc)
- return -ENOMEM;
-
- /* 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 (; 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;
- desc[i-1].next = 0;
-
- /* We're about to use a buffer */
- vq->vq.num_free--;
-
- /* Use a single buffer which doesn't continue */
- head = vq->free_head;
- vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
- vq->vring.desc[head].addr = virt_to_phys(desc);
- /* kmemleak gives a false positive, as it's hidden by virt_to_phys */
- kmemleak_ignore(desc);
- vq->vring.desc[head].len = i * sizeof(struct vring_desc);
-
- /* Update free pointer */
- vq->free_head = vq->vring.desc[head].next;
+ desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
+ if (!desc)
+ return NULL;

- return head;
+ for (i = 0; i < total_sg; i++)
+ desc[i].next = i+1;
+ return desc;
}

static inline int virtqueue_add(struct virtqueue *_vq,
@@ -176,8 +130,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
{
struct vring_virtqueue *vq = to_vvq(_vq);
struct scatterlist *sg;
+ struct vring_desc *desc;
unsigned int i, n, avail, uninitialized_var(prev);
int head;
+ bool indirect;

START_USE(vq);

@@ -201,18 +157,36 @@ static inline int virtqueue_add(struct virtqueue *_vq,
}
#endif

+ BUG_ON(total_sg > vq->vring.num);
+ BUG_ON(total_sg == 0);
+
+ head = vq->free_head;
+
/* 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);
- if (likely(head >= 0))
- goto add_head;
+ if (vq->indirect && total_sg > 1 && vq->vq.num_free)
+ desc = alloc_indirect(total_sg, gfp);
+ else
+ desc = NULL;
+
+ if (desc) {
+ /* Use a single buffer which doesn't continue */
+ vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
+ vq->vring.desc[head].addr = virt_to_phys(desc);
+ /* avoid kmemleak false positive (hidden by virt_to_phys) */
+ kmemleak_ignore(desc);
+ vq->vring.desc[head].len = total_sg * sizeof(struct vring_desc);
+
+ /* Set up rest to use this indirect table. */
+ i = 0;
+ total_sg = 1;
+ indirect = true;
+ } else {
+ desc = vq->vring.desc;
+ i = head;
+ indirect = false;
}

- BUG_ON(total_sg > vq->vring.num);
- BUG_ON(total_sg == 0);
-
if (vq->vq.num_free < total_sg) {
pr_debug("Can't add buf len %i - avail = %i\n",
total_sg, vq->vq.num_free);
@@ -228,32 +202,33 @@ static inline int virtqueue_add(struct virtqueue *_vq,
/* We're about to use some buffers from the free list. */
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;
+ desc[i].flags = VRING_DESC_F_NEXT;
+ desc[i].addr = sg_phys(sg);
+ desc[i].len = sg->length;
prev = i;
- i = vq->vring.desc[i].next;
+ i = desc[i].next;
}
}
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;
+ desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
+ desc[i].addr = sg_phys(sg);
+ desc[i].len = sg->length;
prev = i;
- i = vq->vring.desc[i].next;
+ i = desc[i].next;
}
}
/* Last one doesn't continue. */
- vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
+ desc[prev].flags &= ~VRING_DESC_F_NEXT;

/* Update free pointer */
- vq->free_head = i;
+ if (indirect)
+ vq->free_head = vq->vring.desc[head].next;
+ else
+ vq->free_head = i;

-add_head:
/* Set token. */
vq->data[head] = data;

--
1.9.1

Andy Lutomirski

2014-09-04 01:59:33 UTC

Permalink

Post by Rusty Russell
virtqueue_add() populates the virtqueue descriptor table from the sgs
given. If it uses an indirect descriptor table, then it puts a single
descriptor in the descriptor table pointing to the kmalloc'ed indirect
table where the sg is populated.
Previously vring_add_indirect() did the allocation and the simple
linear layout. We replace that with alloc_indirect() which allocates
the indirect table then chains it like the normal descriptor table so
we can reuse the core logic.
+ if (vq->indirect && total_sg > 1 && vq->vq.num_free)
+ desc = alloc_indirect(total_sg, gfp);
+ else
+ desc = NULL;
+
+ if (desc) {
+ /* Use a single buffer which doesn't continue */
+ vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
+ vq->vring.desc[head].addr = virt_to_phys(desc);
+ /* avoid kmemleak false positive (hidden by virt_to_phys) */
+ kmemleak_ignore(desc);
+ vq->vring.desc[head].len = total_sg * sizeof(struct vring_desc);
+
+ /* Set up rest to use this indirect table. */
+ i = 0;
+ total_sg = 1;

This is a little too magical for me. Would it make sense to add a new
variable for this (total_root_descs or something)?

--Andy

Rusty Russell

2014-09-05 02:55:40 UTC

Permalink

Post by Andy Lutomirski

This is a little too magical for me. Would it make sense to add a new
variable for this (total_root_descs or something)?

Agreed, it's a little hacky.

Here's the diff (I actually merged this into the patch, but no point
re-xmitting):

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a4ebbffac141..6d2b5310c991 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -131,7 +131,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
struct vring_virtqueue *vq = to_vvq(_vq);
struct scatterlist *sg;
struct vring_desc *desc;
- unsigned int i, n, avail, uninitialized_var(prev);
+ unsigned int i, n, avail, descs_used, uninitialized_var(prev);
int head;
bool indirect;

@@ -179,17 +179,18 @@ static inline int virtqueue_add(struct virtqueue *_vq,

/* Set up rest to use this indirect table. */
i = 0;
- total_sg = 1;
+ descs_used = 1;
indirect = true;
} else {
desc = vq->vring.desc;
i = head;
+ descs_used = total_sg;
indirect = false;
}

- if (vq->vq.num_free < total_sg) {
+ if (vq->vq.num_free < descs_used) {
pr_debug("Can't add buf len %i - avail = %i\n",
- total_sg, vq->vq.num_free);
+ descs_used, 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. */
@@ -200,7 +201,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
}

/* We're about to use some buffers from the free list. */
- vq->vq.num_free -= total_sg;
+ vq->vq.num_free -= descs_used;

for (n = 0; n < out_sgs; n++) {
for (sg = sgs[n]; sg; sg = sg_next(sg)) {

Paolo Bonzini

2014-09-05 10:55:37 UTC

Permalink

Post by Rusty Russell
+ desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
+ if (!desc)
+ return NULL;
- return head;
+ for (i = 0; i < total_sg; i++)
+ desc[i].next = i+1;
+ return desc;
}

Would it make sense to keep a cache of a few (say) 8- or 16-element
indirect descriptors? You'd only have to do this ugly (and slowish) for
loop on the first allocation.

Also, since this is mostly an aesthetic patch,

Post by Rusty Russell
+ if (indirect)
+ vq->free_head = vq->vring.desc[head].next;
+ else
+ vq->free_head = i;

I'd move the indirect case above, where the vring.desc[head] is actually
allocated.

Paolo

Andy Lutomirski

2014-09-08 17:32:07 UTC

Permalink

Post by Paolo Bonzini

+ desc = kmalloc(total_sg * sizeof(struct vring_desc), gfp);
+ if (!desc)
+ return NULL;
- return head;
+ for (i = 0; i < total_sg; i++)
+ desc[i].next = i+1;
+ return desc;
}

+ if (indirect)
+ vq->free_head = vq->vring.desc[head].next;
+ else
+ vq->free_head = i;

I'd move the indirect case above, where the vring.desc[head] is actually
allocated.

Please don't: I'll just have to undo it for the DMA API stuff, since
descriptor setup will be able to fail.

--Andy

Rusty Russell

2014-09-03 04:29:15 UTC

Permalink

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 at rustcorp.com.au>
---
drivers/virtio/virtio_ring.c | 68 +++++++++++++-------------------------------
1 file changed, 19 insertions(+), 49 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 4d08f45a9c29..374399c62080 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -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)
@@ -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;
@@ -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;
@@ -186,10 +168,7 @@ 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,
@@ -197,7 +176,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
{
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);
@@ -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;
@@ -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;
@@ -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;
@@ -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).
*
@@ -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).
*
@@ -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);

--
1.9.1

Andy Lutomirski

2014-09-03 04:54:11 UTC

Permalink

Post by Rusty Russell
This is the only driver which doesn't hand virtqueue_add_inbuf and
virtqueue_add_outbuf a well-formed, well-terminated sg. Fix it,
so we can make virtio_add_* simpler.

OK, I get it now: you're reinitializing the table every time, clearing
old end marks. There's room to microoptimize this, but it's probably
not worth it.

IOW, looks good to me.

--Andy

Paolo Bonzini

2014-09-05 10:40:50 UTC

Permalink

Post by Rusty Russell
+ sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);

I think 2 is enough here. That said...

Post by Rusty Russell
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
-
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);

... skb_to_sgvec will already make the sg well formed, so the
sg_init_table is _almost_ redundant; it is only there to remove
intermediate end marks. The block layer takes care to remove
them, but skb_to_sgvec doesn't.

If the following patch can be accepted to net/core/skbuff.c, the
sg_init_table in virtnet_alloc_queues will suffice.

Paolo

-------------------- 8< -------------------
From: Paolo Bonzini <pbonzini at redhat.com>
Subject: [PATCH] net: skb_to_sgvec: do not leave intermediate marks in the sgvec

sg_set_buf/sg_set_page will leave the end mark in place in their
argument, which may be in the middle of a scatterlist. If we
remove the mark before calling them, we can avoid calls to
sg_init_table before skb_to_sgvec.

However, users of skb_to_sgvec_nomark now need to be careful and
possibly restore the mark.

Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 163b673f9e62..a3108ef1f1c0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3265,6 +3265,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
if (copy > 0) {
if (copy > len)
copy = len;
+ sg_unmark_end(sg);
sg_set_buf(sg, skb->data + offset, copy);
elt++;
if ((len -= copy) == 0)
@@ -3283,6 +3284,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)

if (copy > len)
copy = len;
+ sg_unmark_end(&sg[elt]);
sg_set_page(&sg[elt], skb_frag_page(frag), copy,
frag->page_offset+offset-start);
elt++;
@@ -3322,7 +3324,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
* Scenario to use skb_to_sgvec_nomark:
* 1. sg_init_table
* 2. skb_to_sgvec_nomark(payload1)
- * 3. skb_to_sgvec_nomark(payload2)
+ * 3. skb_to_sgvec(payload2)
*
* This is equivalent to:
* 1. sg_init_table
diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index a2afa89513a0..9ae5756d9e5f 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -227,6 +227,7 @@ static int ah_output(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah_output_done, skb);

@@ -395,6 +396,7 @@ static int ah_input(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah_input_done, skb);

diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index 72a4930bdc0a..c680d82e43de 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -430,6 +430,8 @@ static int ah6_output(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
+
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah6_output_done, skb);

@@ -608,6 +610,7 @@ static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);

ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah6_input_done, skb);

Michael S. Tsirkin

2014-09-07 07:20:32 UTC

Permalink

Post by Paolo Bonzini

Post by Rusty Russell
+ sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);

I think 2 is enough here. That said...

Post by Rusty Russell
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
-
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);

You will have to post it to netdev as a new topic and Cc
Dave Miller for it to be considered.

Post by Paolo Bonzini
-------------------- 8< -------------------
From: Paolo Bonzini <pbonzini at redhat.com>
Subject: [PATCH] net: skb_to_sgvec: do not leave intermediate marks in the sgvec
sg_set_buf/sg_set_page will leave the end mark in place in their
argument, which may be in the middle of a scatterlist. If we
remove the mark before calling them, we can avoid calls to
sg_init_table before skb_to_sgvec.
However, users of skb_to_sgvec_nomark now need to be careful and
possibly restore the mark.
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 163b673f9e62..a3108ef1f1c0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3265,6 +3265,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
if (copy > 0) {
if (copy > len)
copy = len;
+ sg_unmark_end(sg);
sg_set_buf(sg, skb->data + offset, copy);
elt++;
if ((len -= copy) == 0)
@@ -3283,6 +3284,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
if (copy > len)
copy = len;
+ sg_unmark_end(&sg[elt]);
sg_set_page(&sg[elt], skb_frag_page(frag), copy,
frag->page_offset+offset-start);
elt++;
@@ -3322,7 +3324,7 @@ __skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
* 1. sg_init_table
* 2. skb_to_sgvec_nomark(payload1)
- * 3. skb_to_sgvec_nomark(payload2)
+ * 3. skb_to_sgvec(payload2)
*
* 1. sg_init_table
diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
index a2afa89513a0..9ae5756d9e5f 100644
--- a/net/ipv4/ah4.c
+++ b/net/ipv4/ah4.c
@@ -227,6 +227,7 @@ static int ah_output(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah_output_done, skb);
@@ -395,6 +396,7 @@ static int ah_input(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah_input_done, skb);
diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index 72a4930bdc0a..c680d82e43de 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -430,6 +430,8 @@ static int ah6_output(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = htonl(XFRM_SKB_CB(skb)->seq.output.hi);
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
+
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah6_output_done, skb);
@@ -608,6 +610,7 @@ static int ah6_input(struct xfrm_state *x, struct sk_buff *skb)
*seqhi = XFRM_SKB_CB(skb)->seq.input.hi;
sg_set_buf(seqhisg, seqhi, seqhi_len);
}
+ sg_mark_end(&sg[nfrags + sglists]);
ahash_request_set_crypt(req, sg, icv, skb->len + seqhi_len);
ahash_request_set_callback(req, 0, ah6_input_done, skb);

Rusty Russell

2014-10-14 02:21:47 UTC

Permalink

Post by Paolo Bonzini

Post by Rusty Russell
+ sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);

I think 2 is enough here. That said...

Post by Rusty Russell
sg_set_buf(rq->sg, &hdr->hdr, sizeof hdr->hdr);
-
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);

sg_init_table is still needed if CONFIG_DEBUG_SG, so I don't
think it's worth it.

Thanks,
Rusty.

Jesper Dangaard Brouer

2014-09-03 10:23:50 UTC

Permalink

On Wed, 3 Sep 2014 13:59:14 +0930

Post by Rusty Russell
modprobe pktgen
echo 'add_device eth0' > /proc/net/pktgen/kpktgend_0
echo nowait 1 > /proc/net/pktgen/eth0

Maybe your pktgen "nowait" (patch) should be a flag instead?

echo "flag EXIT_NO_WAIT" > /proc/net/pktgen/eth0

Post by Rusty Russell
echo count 1000000 > /proc/net/pktgen/eth0
echo clone_skb 100000 > /proc/net/pktgen/eth0
echo dst_mac 4e:14:25:a9:30:ac > /proc/net/pktgen/eth0
echo dst 192.168.1.2 > /proc/net/pktgen/eth0
for i in `seq 20`; do echo start > /proc/net/pktgen/pgctrl; tail -n1 /proc/net/pktgen/eth0; done

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Sr. Network Kernel Developer at Red Hat
Author of http://www.iptv-analyzer.org
LinkedIn: http://www.linkedin.com/in/brouer

David Miller

2014-09-05 21:27:45 UTC

Permalink

From: Rusty Russell <rusty at rustcorp.com.au>
Date: Wed, 3 Sep 2014 13:59:13 +0930

I resurrected these patches after prompting from Andy Lutomirski's
recent patches. I put them on the back-burner because vring_bench
had a 15% slowdown on my laptop: pktgen testing revealed a speedup,
if anything, so I've cleaned them up.

If you want to merge this via your virtio tree that's fine with me.

For virtio_net:

Acked-by: David S. Miller <davem at davemloft.net>