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libeth: xdp, xsk: access adjacent u32s as u64 where applicable

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On 64-bit systems, writing/reading one u64 is faster than two u32s even
when they're are adjacent in a struct. The compilers won't guarantee
they will combine those; I observed both successful and unsuccessful
attempts with both GCC and Clang, and it's not easy to say what it
depends on.
There's a few places in libeth_xdp winning up to several percent from
combined access (both performance and object code size, especially
when unrolling). Add __LIBETH_WORD_ACCESS and use it there on LE.
Drivers are free to optimize HW-specific callbacks under the same
definition.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
This commit is contained in:
Alexander Lobakin 2025-06-12 18:02:34 +02:00 committed by Tony Nguyen
parent 3ced71a8b3
commit 80bae9df21
2 changed files with 31 additions and 8 deletions
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29
include/net/libeth/xdp.h
View File

@ -475,6 +475,21 @@ struct libeth_xdp_tx_desc {
((const void *)(uintptr_t)(priv)); \
})
/*
* On 64-bit systems, assigning one u64 is faster than two u32s. When ::len
* occupies lowest 32 bits (LE), whole ::opts can be assigned directly instead.
*/
#ifdef __LITTLE_ENDIAN
#define __LIBETH_WORD_ACCESS 1
#endif
#ifdef __LIBETH_WORD_ACCESS
#define __libeth_xdp_tx_len(flen, ...) \
.opts = ((flen) | FIELD_PREP(GENMASK_ULL(63, 32), (__VA_ARGS__ + 0)))
#else
#define __libeth_xdp_tx_len(flen, ...) \
.len = (flen), .flags = (__VA_ARGS__ + 0)
#endif
/**
* libeth_xdp_tx_xmit_bulk - main XDP Tx function
* @bulk: array of frames to send
@ -870,8 +885,7 @@ static inline u32 libeth_xdp_xmit_queue_head(struct libeth_xdp_tx_bulk *bq,
bq->bulk[bq->count++] = (typeof(*bq->bulk)){
.xdpf = xdpf,
.len = xdpf->len,
.flags = LIBETH_XDP_TX_FIRST,
__libeth_xdp_tx_len(xdpf->len, LIBETH_XDP_TX_FIRST),
};
if (!xdp_frame_has_frags(xdpf))
@ -902,7 +916,7 @@ static inline bool libeth_xdp_xmit_queue_frag(struct libeth_xdp_tx_bulk *bq,
bq->bulk[bq->count++] = (typeof(*bq->bulk)){
.dma = dma,
.len = skb_frag_size(frag),
__libeth_xdp_tx_len(skb_frag_size(frag)),
};
return true;
@ -1260,6 +1274,7 @@ bool libeth_xdp_buff_add_frag(struct libeth_xdp_buff *xdp,
* Internal, use libeth_xdp_process_buff() instead. Initializes XDP buffer
* head with the Rx buffer data: data pointer, length, headroom, and
* truesize/tailroom. Zeroes the flags.
* Uses faster single u64 write instead of per-field access.
*/
static inline void libeth_xdp_prepare_buff(struct libeth_xdp_buff *xdp,
const struct libeth_fqe *fqe,
@ -1267,7 +1282,15 @@ static inline void libeth_xdp_prepare_buff(struct libeth_xdp_buff *xdp,
{
const struct page *page = __netmem_to_page(fqe->netmem);
#ifdef __LIBETH_WORD_ACCESS
static_assert(offsetofend(typeof(xdp->base), flags) -
offsetof(typeof(xdp->base), frame_sz) ==
sizeof(u64));
*(u64 *)&xdp->base.frame_sz = fqe->truesize;
#else
xdp_init_buff(&xdp->base, fqe->truesize, xdp->base.rxq);
#endif
xdp_prepare_buff(&xdp->base, page_address(page) + fqe->offset,
page->pp->p.offset, len, true);
}

10
include/net/libeth/xsk.h
View File

@ -26,8 +26,8 @@ static inline bool libeth_xsk_tx_queue_head(struct libeth_xdp_tx_bulk *bq,
{
bq->bulk[bq->count++] = (typeof(*bq->bulk)){
.xsk = xdp,
.len = xdp->base.data_end - xdp->data,
.flags = LIBETH_XDP_TX_FIRST,
__libeth_xdp_tx_len(xdp->base.data_end - xdp->data,
LIBETH_XDP_TX_FIRST),
};
if (likely(!xdp_buff_has_frags(&xdp->base)))
@ -48,7 +48,7 @@ static inline void libeth_xsk_tx_queue_frag(struct libeth_xdp_tx_bulk *bq,
{
bq->bulk[bq->count++] = (typeof(*bq->bulk)){
.xsk = frag,
.len = frag->base.data_end - frag->data,
__libeth_xdp_tx_len(frag->base.data_end - frag->data),
};
}
@ -199,7 +199,7 @@ __libeth_xsk_xmit_fill_buf_md(const struct xdp_desc *xdesc,
ctx = xsk_buff_raw_get_ctx(sq->pool, xdesc->addr);
desc = (typeof(desc)){
.addr = ctx.dma,
.len = xdesc->len,
__libeth_xdp_tx_len(xdesc->len),
};
BUILD_BUG_ON(!__builtin_constant_p(tmo == libeth_xsktmo));
@ -226,7 +226,7 @@ __libeth_xsk_xmit_fill_buf(const struct xdp_desc *xdesc,
{
return (struct libeth_xdp_tx_desc){
.addr = xsk_buff_raw_get_dma(sq->pool, xdesc->addr),
.len = xdesc->len,
__libeth_xdp_tx_len(xdesc->len),
};
}