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@xxxxxxxxx>
---
include/net/libeth/xdp.h | 29 ++++++++++++++++++++++++++---
include/net/libeth/xsk.h | 10 +++++-----
2 files changed, 31 insertions(+), 8 deletions(-)
diff --git a/include/net/libeth/xdp.h b/include/net/libeth/xdp.h
index 85f058482fc7..6d15386aff31 100644
--- a/include/net/libeth/xdp.h
+++ b/include/net/libeth/xdp.h
@@ -464,6 +464,21 @@ 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
@@ -863,8 +878,7 @@ 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))
@@ -895,7 +909,7 @@ 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;
@@ -1253,6 +1267,7 @@ 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,
@@ -1260,7 +1275,15 @@ 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);
}
diff --git a/include/net/libeth/xsk.h b/include/net/libeth/xsk.h
index 213778a68476..481a7b28e6f2 100644
--- a/include/net/libeth/xsk.h
+++ b/include/net/libeth/xsk.h
@@ -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),
};
}
--
2.49.0
