linux/net/xdp/xsk_queue.c
Björn Töpel bbff2f321a xsk: new descriptor addressing scheme
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>
2018-06-04 17:21:02 +02:00

64 lines
1.2 KiB
C

// SPDX-License-Identifier: GPL-2.0
/* XDP user-space ring structure
* Copyright(c) 2018 Intel Corporation.
*/
#include <linux/slab.h>
#include "xsk_queue.h"
void xskq_set_umem(struct xsk_queue *q, struct xdp_umem_props *umem_props)
{
if (!q)
return;
q->umem_props = *umem_props;
}
static u32 xskq_umem_get_ring_size(struct xsk_queue *q)
{
return sizeof(struct xdp_umem_ring) + q->nentries * sizeof(u64);
}
static u32 xskq_rxtx_get_ring_size(struct xsk_queue *q)
{
return sizeof(struct xdp_ring) + q->nentries * sizeof(struct xdp_desc);
}
struct xsk_queue *xskq_create(u32 nentries, bool umem_queue)
{
struct xsk_queue *q;
gfp_t gfp_flags;
size_t size;
q = kzalloc(sizeof(*q), GFP_KERNEL);
if (!q)
return NULL;
q->nentries = nentries;
q->ring_mask = nentries - 1;
gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN |
__GFP_COMP | __GFP_NORETRY;
size = umem_queue ? xskq_umem_get_ring_size(q) :
xskq_rxtx_get_ring_size(q);
q->ring = (struct xdp_ring *)__get_free_pages(gfp_flags,
get_order(size));
if (!q->ring) {
kfree(q);
return NULL;
}
return q;
}
void xskq_destroy(struct xsk_queue *q)
{
if (!q)
return;
page_frag_free(q->ring);
kfree(q);
}