From: Stefan Metzmacher <metze@xxxxxxxxx> commit e307e6698165ca6508ed42c69cb1be76c8eb6a3c upstream. It might be useful for applications to detect if a zero copy transfer with SEND[MSG]_ZC was actually possible or not. The application can fallback to plain SEND[MSG] in order to avoid the overhead of two cqes per request. Or it can generate a log message that could indicate to an administrator that no zero copy was possible and could explain degraded performance. Cc: stable@xxxxxxxxxxxxxxx # 6.1 Link: https://lore.kernel.org/io-uring/fb6a7599-8a9b-15e5-9b64-6cd9d01c6ff4@xxxxxxxxx/T/#m2b0d9df94ce43b0e69e6c089bdff0ce6babbdfaa Signed-off-by: Stefan Metzmacher <metze@xxxxxxxxx> Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx> Link: https://lore.kernel.org/r/8945b01756d902f5d5b0667f20b957ad3f742e5e.1666895626.git.metze@xxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/uapi/linux/io_uring.h | 18 ++++++++++++++++++ io_uring/net.c | 6 +++++- io_uring/notif.c | 12 ++++++++++++ io_uring/notif.h | 3 +++ 4 files changed, 38 insertions(+), 1 deletion(-) --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -296,10 +296,28 @@ enum io_uring_op { * * IORING_RECVSEND_FIXED_BUF Use registered buffers, the index is stored in * the buf_index field. + * + * IORING_SEND_ZC_REPORT_USAGE + * If set, SEND[MSG]_ZC should report + * the zerocopy usage in cqe.res + * for the IORING_CQE_F_NOTIF cqe. + * 0 is reported if zerocopy was actually possible. + * IORING_NOTIF_USAGE_ZC_COPIED if data was copied + * (at least partially). */ #define IORING_RECVSEND_POLL_FIRST (1U << 0) #define IORING_RECV_MULTISHOT (1U << 1) #define IORING_RECVSEND_FIXED_BUF (1U << 2) +#define IORING_SEND_ZC_REPORT_USAGE (1U << 3) + +/* + * cqe.res for IORING_CQE_F_NOTIF if + * IORING_SEND_ZC_REPORT_USAGE was requested + * + * It should be treated as a flag, all other + * bits of cqe.res should be treated as reserved! + */ +#define IORING_NOTIF_USAGE_ZC_COPIED (1U << 31) /* * accept flags stored in sqe->ioprio --- a/io_uring/net.c +++ b/io_uring/net.c @@ -937,7 +937,8 @@ int io_send_zc_prep(struct io_kiocb *req zc->flags = READ_ONCE(sqe->ioprio); if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | - IORING_RECVSEND_FIXED_BUF)) + IORING_RECVSEND_FIXED_BUF | + IORING_SEND_ZC_REPORT_USAGE)) return -EINVAL; notif = zc->notif = io_alloc_notif(ctx); if (!notif) @@ -955,6 +956,9 @@ int io_send_zc_prep(struct io_kiocb *req req->imu = READ_ONCE(ctx->user_bufs[idx]); io_req_set_rsrc_node(notif, ctx, 0); } + if (zc->flags & IORING_SEND_ZC_REPORT_USAGE) { + io_notif_to_data(notif)->zc_report = true; + } if (req->opcode == IORING_OP_SEND_ZC) { if (READ_ONCE(sqe->__pad3[0])) --- a/io_uring/notif.c +++ b/io_uring/notif.c @@ -18,6 +18,10 @@ static void __io_notif_complete_tw(struc __io_unaccount_mem(ctx->user, nd->account_pages); nd->account_pages = 0; } + + if (nd->zc_report && (nd->zc_copied || !nd->zc_used)) + notif->cqe.res |= IORING_NOTIF_USAGE_ZC_COPIED; + io_req_task_complete(notif, locked); } @@ -28,6 +32,13 @@ static void io_uring_tx_zerocopy_callbac struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg); struct io_kiocb *notif = cmd_to_io_kiocb(nd); + if (nd->zc_report) { + if (success && !nd->zc_used && skb) + WRITE_ONCE(nd->zc_used, true); + else if (!success && !nd->zc_copied) + WRITE_ONCE(nd->zc_copied, true); + } + if (refcount_dec_and_test(&uarg->refcnt)) { notif->io_task_work.func = __io_notif_complete_tw; io_req_task_work_add(notif); @@ -55,6 +66,7 @@ struct io_kiocb *io_alloc_notif(struct i nd->account_pages = 0; nd->uarg.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN; nd->uarg.callback = io_uring_tx_zerocopy_callback; + nd->zc_report = nd->zc_used = nd->zc_copied = false; refcount_set(&nd->uarg.refcnt, 1); return notif; } --- a/io_uring/notif.h +++ b/io_uring/notif.h @@ -13,6 +13,9 @@ struct io_notif_data { struct file *file; struct ubuf_info uarg; unsigned long account_pages; + bool zc_report; + bool zc_used; + bool zc_copied; }; void io_notif_flush(struct io_kiocb *notif);
