[PATCH v2 for-next 10/12] io_uring: multishot recv
From: Dylan Yudaken
Date: Thu Jun 30 2022 - 05:19:19 EST
Support multishot receive for io_uring.
Typical server applications will run a loop where for each recv CQE it
requeues another recv/recvmsg.
This can be simplified by using the existing multishot functionality
combined with io_uring's provided buffers.
The API is to add the IORING_RECV_MULTISHOT flag to the SQE. CQEs will
then be posted (with IORING_CQE_F_MORE flag set) when data is available
and is read. Once an error occurs or the socket ends, the multishot will
be removed and a completion without IORING_CQE_F_MORE will be posted.
The benefit to this is that the recv is much more performant.
* Subsequent receives are queued up straight away without requiring the
application to finish a processing loop.
* If there are more data in the socket (sat the provided buffer size is
smaller than the socket buffer) then the data is immediately
returned, improving batching.
* Poll is only armed once and reused, saving CPU cycles
Signed-off-by: Dylan Yudaken <dylany@xxxxxx>
---
include/uapi/linux/io_uring.h | 5 ++
io_uring/net.c | 102 +++++++++++++++++++++++++++++-----
2 files changed, 94 insertions(+), 13 deletions(-)
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 05addde13df8..405bb5a67d47 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -260,8 +260,13 @@ enum io_uring_op {
* or receive and arm poll if that yields an
* -EAGAIN result, arm poll upfront and skip
* the initial transfer attempt.
+ *
+ * IORING_RECV_MULTISHOT Multishot recv. Sets IORING_CQE_F_MORE if
+ * the handler will continue to report
+ * CQEs on behalf of the same SQE.
*/
#define IORING_RECVSEND_POLL_FIRST (1U << 0)
+#define IORING_RECV_MULTISHOT (1U << 1)
/*
* accept flags stored in sqe->ioprio
diff --git a/io_uring/net.c b/io_uring/net.c
index 75761f48c959..3394825f74fd 100644
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -389,6 +389,8 @@ int io_recvmsg_prep_async(struct io_kiocb *req)
return ret;
}
+#define RECVMSG_FLAGS (IORING_RECVSEND_POLL_FIRST | IORING_RECV_MULTISHOT)
+
int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
struct io_sr_msg *sr = io_kiocb_to_cmd(req);
@@ -399,13 +401,22 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
sr->umsg = u64_to_user_ptr(READ_ONCE(sqe->addr));
sr->len = READ_ONCE(sqe->len);
sr->flags = READ_ONCE(sqe->addr2);
- if (sr->flags & ~IORING_RECVSEND_POLL_FIRST)
+ if (sr->flags & ~(RECVMSG_FLAGS))
return -EINVAL;
sr->msg_flags = READ_ONCE(sqe->msg_flags) | MSG_NOSIGNAL;
if (sr->msg_flags & MSG_DONTWAIT)
req->flags |= REQ_F_NOWAIT;
if (sr->msg_flags & MSG_ERRQUEUE)
req->flags |= REQ_F_CLEAR_POLLIN;
+ if (sr->flags & IORING_RECV_MULTISHOT) {
+ if (!(req->flags & REQ_F_BUFFER_SELECT))
+ return -EINVAL;
+ if (sr->msg_flags & MSG_WAITALL)
+ return -EINVAL;
+ if (req->opcode == IORING_OP_RECV && sr->len)
+ return -EINVAL;
+ req->flags |= REQ_F_APOLL_MULTISHOT;
+ }
#ifdef CONFIG_COMPAT
if (req->ctx->compat)
@@ -415,6 +426,48 @@ int io_recvmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
return 0;
}
+static inline void io_recv_prep_retry(struct io_kiocb *req)
+{
+ struct io_sr_msg *sr = io_kiocb_to_cmd(req);
+
+ sr->done_io = 0;
+ sr->len = 0; /* get from the provided buffer */
+}
+
+/*
+ * Finishes io_recv and io_recvmsg.
+ *
+ * Returns true if it is actually finished, or false if it should run
+ * again (for multishot).
+ */
+static inline bool io_recv_finish(struct io_kiocb *req, int *ret, unsigned int cflags)
+{
+ if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
+ io_req_set_res(req, *ret, cflags);
+ *ret = IOU_OK;
+ return true;
+ }
+
+ if (*ret > 0) {
+ if (io_post_aux_cqe(req->ctx, req->cqe.user_data, *ret,
+ cflags | IORING_CQE_F_MORE, false)) {
+ io_recv_prep_retry(req);
+ return false;
+ }
+ /*
+ * Otherwise stop multishot but use the current result.
+ * Probably will end up going into overflow, but this means
+ * we cannot trust the ordering anymore
+ */
+ }
+
+ io_req_set_res(req, *ret, cflags);
+
+ if (req->flags & REQ_F_POLLED)
+ *ret = IOU_STOP_MULTISHOT;
+ return true;
+}
+
int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_sr_msg *sr = io_kiocb_to_cmd(req);
@@ -424,6 +477,7 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
unsigned flags;
int ret, min_ret = 0;
bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+ size_t len = sr->len;
sock = sock_from_file(req->file);
if (unlikely(!sock))
@@ -442,16 +496,17 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
(sr->flags & IORING_RECVSEND_POLL_FIRST))
return io_setup_async_msg(req, kmsg);
+retry_multishot:
if (io_do_buffer_select(req)) {
void __user *buf;
- buf = io_buffer_select(req, &sr->len, issue_flags);
+ buf = io_buffer_select(req, &len, issue_flags);
if (!buf)
return -ENOBUFS;
kmsg->fast_iov[0].iov_base = buf;
- kmsg->fast_iov[0].iov_len = sr->len;
+ kmsg->fast_iov[0].iov_len = len;
iov_iter_init(&kmsg->msg.msg_iter, READ, kmsg->fast_iov, 1,
- sr->len);
+ len);
}
flags = sr->msg_flags;
@@ -463,8 +518,15 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
kmsg->msg.msg_get_inq = 1;
ret = __sys_recvmsg_sock(sock, &kmsg->msg, sr->umsg, kmsg->uaddr, flags);
if (ret < min_ret) {
- if (ret == -EAGAIN && force_nonblock)
- return io_setup_async_msg(req, kmsg);
+ if (ret == -EAGAIN && force_nonblock) {
+ ret = io_setup_async_msg(req, kmsg);
+ if (ret == -EAGAIN && (req->flags & IO_APOLL_MULTI_POLLED) ==
+ IO_APOLL_MULTI_POLLED) {
+ io_kbuf_recycle(req, issue_flags);
+ return IOU_ISSUE_SKIP_COMPLETE;
+ }
+ return ret;
+ }
if (ret == -ERESTARTSYS)
ret = -EINTR;
if (ret > 0 && io_net_retry(sock, flags)) {
@@ -491,8 +553,11 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
cflags = io_put_kbuf(req, issue_flags);
if (kmsg->msg.msg_inq)
cflags |= IORING_CQE_F_SOCK_NONEMPTY;
- io_req_set_res(req, ret, cflags);
- return IOU_OK;
+
+ if (!io_recv_finish(req, &ret, cflags))
+ goto retry_multishot;
+
+ return ret;
}
int io_recv(struct io_kiocb *req, unsigned int issue_flags)
@@ -505,6 +570,7 @@ int io_recv(struct io_kiocb *req, unsigned int issue_flags)
unsigned flags;
int ret, min_ret = 0;
bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+ size_t len = sr->len;
if (!(req->flags & REQ_F_POLLED) &&
(sr->flags & IORING_RECVSEND_POLL_FIRST))
@@ -514,16 +580,17 @@ int io_recv(struct io_kiocb *req, unsigned int issue_flags)
if (unlikely(!sock))
return -ENOTSOCK;
+retry_multishot:
if (io_do_buffer_select(req)) {
void __user *buf;
- buf = io_buffer_select(req, &sr->len, issue_flags);
+ buf = io_buffer_select(req, &len, issue_flags);
if (!buf)
return -ENOBUFS;
sr->buf = buf;
}
- ret = import_single_range(READ, sr->buf, sr->len, &iov, &msg.msg_iter);
+ ret = import_single_range(READ, sr->buf, len, &iov, &msg.msg_iter);
if (unlikely(ret))
goto out_free;
@@ -543,8 +610,14 @@ int io_recv(struct io_kiocb *req, unsigned int issue_flags)
ret = sock_recvmsg(sock, &msg, flags);
if (ret < min_ret) {
- if (ret == -EAGAIN && force_nonblock)
+ if (ret == -EAGAIN && force_nonblock) {
+ if ((req->flags & IO_APOLL_MULTI_POLLED) == IO_APOLL_MULTI_POLLED) {
+ io_kbuf_recycle(req, issue_flags);
+ return IOU_ISSUE_SKIP_COMPLETE;
+ }
+
return -EAGAIN;
+ }
if (ret == -ERESTARTSYS)
ret = -EINTR;
if (ret > 0 && io_net_retry(sock, flags)) {
@@ -570,8 +643,11 @@ int io_recv(struct io_kiocb *req, unsigned int issue_flags)
cflags = io_put_kbuf(req, issue_flags);
if (msg.msg_inq)
cflags |= IORING_CQE_F_SOCK_NONEMPTY;
- io_req_set_res(req, ret, cflags);
- return IOU_OK;
+
+ if (!io_recv_finish(req, &ret, cflags))
+ goto retry_multishot;
+
+ return ret;
}
int io_accept_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
--
2.30.2