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xsk: new descriptor addressing scheme

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Currently, AF_XDP only supports a fixed frame-size memory scheme where
each frame is referenced via an index (idx). A user passes the frame
index to the kernel, and the kernel acts upon the data.  Some NICs,
however, do not have a fixed frame-size model, instead they have a
model where a memory window is passed to the hardware and multiple
frames are filled into that window (referred to as the "type-writer"
model).

By changing the descriptor format from the current frame index
addressing scheme, AF_XDP can in the future be extended to support
these kinds of NICs.

In the index-based model, an idx refers to a frame of size
frame_size. Addressing a frame in the UMEM is done by offseting the
UMEM starting address by a global offset, idx * frame_size + offset.
Communicating via the fill- and completion-rings are done by means of
idx.

In this commit, the idx is removed in favor of an address (addr),
which is a relative address ranging over the UMEM. To convert an
idx-based address to the new addr is simply: addr = idx * frame_size +
offset.

We also stop referring to the UMEM "frame" as a frame. Instead it is
simply called a chunk.

To transfer ownership of a chunk to the kernel, the addr of the chunk
is passed in the fill-ring. Note, that the kernel will mask addr to
make it chunk aligned, so there is no need for userspace to do
that. E.g., for a chunk size of 2k, passing an addr of 2048, 2050 or
3000 to the fill-ring will refer to the same chunk.

On the completion-ring, the addr will match that of the Tx descriptor,
passed to the kernel.

Changing the descriptor format to use chunks/addr will allow for
future changes to move to a type-writer based model, where multiple
frames can reside in one chunk. In this model passing one single chunk
into the fill-ring, would potentially result in multiple Rx
descriptors.

This commit changes the uapi of AF_XDP sockets, and updates the
documentation.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Björn Töpel
2018-06-04 13:57:13 +02:00
committed by Daniel Borkmann
parent a509a95536
commit bbff2f321a
8 changed files with 123 additions and 129 deletions
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30
net/xdp/xsk.c
View File

@@ -41,24 +41,27 @@ bool xsk_is_setup_for_bpf_map(struct xdp_sock *xs)
static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
{
u32 id, len = xdp->data_end - xdp->data;
u32 len = xdp->data_end - xdp->data;
void *buffer;
u64 addr;
int err;
if (xs->dev != xdp->rxq->dev || xs->queue_id != xdp->rxq->queue_index)
return -EINVAL;
if (!xskq_peek_id(xs->umem->fq, &id)) {
if (!xskq_peek_addr(xs->umem->fq, &addr) ||
len > xs->umem->chunk_size_nohr) {
xs->rx_dropped++;
return -ENOSPC;
}
buffer = xdp_umem_get_data_with_headroom(xs->umem, id);
addr += xs->umem->headroom;
buffer = xdp_umem_get_data(xs->umem, addr);
memcpy(buffer, xdp->data, len);
err = xskq_produce_batch_desc(xs->rx, id, len,
xs->umem->frame_headroom);
err = xskq_produce_batch_desc(xs->rx, addr, len);
if (!err)
xskq_discard_id(xs->umem->fq);
xskq_discard_addr(xs->umem->fq);
else
xs->rx_dropped++;
@@ -95,10 +98,10 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
static void xsk_destruct_skb(struct sk_buff *skb)
{
u32 id = (u32)(long)skb_shinfo(skb)->destructor_arg;
u64 addr = (u64)(long)skb_shinfo(skb)->destructor_arg;
struct xdp_sock *xs = xdp_sk(skb->sk);
WARN_ON_ONCE(xskq_produce_id(xs->umem->cq, id));
WARN_ON_ONCE(xskq_produce_addr(xs->umem->cq, addr));
sock_wfree(skb);
}
@@ -123,14 +126,15 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
while (xskq_peek_desc(xs->tx, &desc)) {
char *buffer;
u32 id, len;
u64 addr;
u32 len;
if (max_batch-- == 0) {
err = -EAGAIN;
goto out;
}
if (xskq_reserve_id(xs->umem->cq)) {
if (xskq_reserve_addr(xs->umem->cq)) {
err = -EAGAIN;
goto out;
}
@@ -153,8 +157,8 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
}
skb_put(skb, len);
id = desc.idx;
buffer = xdp_umem_get_data(xs->umem, id) + desc.offset;
addr = desc.addr;
buffer = xdp_umem_get_data(xs->umem, addr);
err = skb_store_bits(skb, 0, buffer, len);
if (unlikely(err)) {
kfree_skb(skb);
@@ -164,7 +168,7 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
skb->dev = xs->dev;
skb->priority = sk->sk_priority;
skb->mark = sk->sk_mark;
skb_shinfo(skb)->destructor_arg = (void *)(long)id;
skb_shinfo(skb)->destructor_arg = (void *)(long)addr;
skb->destructor = xsk_destruct_skb;
err = dev_direct_xmit(skb, xs->queue_id);