If IORING_SETUP_DEFER_TASKRUN is set, then we can't post CQEs remotely
to the target ring. Instead, task_work is queued for the target ring,
which is used to post the CQE. To make matters worse, once the target
CQE has been posted, task_work is then queued with the originator to
fill the completion.
This obviously adds a bunch of overhead and latency. Instead of relying
on generic kernel task_work for this, fill an overflow entry on the
target ring and flag it as such that the target ring will flush it. This
avoids both the task_work for posting the CQE, and it means that the
originator CQE can be filled inline as well.
In local testing, this reduces the latency on the sender side by 5-6x.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
io_uring/msg_ring.c | 88 ++++++++++++++++++++++++++++-----------------
1 file changed, 56 insertions(+), 32 deletions(-)
diff --git a/io_uring/msg_ring.c b/io_uring/msg_ring.c
index 9fdb0cc19bfd..2b649087fe5c 100644
--- a/io_uring/msg_ring.c
+++ b/io_uring/msg_ring.c
@@ -87,38 +87,62 @@ static int io_msg_exec_remote(struct io_kiocb *req, task_work_func_t func)
return IOU_ISSUE_SKIP_COMPLETE;
}
-static void io_msg_tw_complete(struct callback_head *head)
+static struct io_overflow_cqe *io_alloc_overflow(struct io_ring_ctx *target_ctx)
{
- struct io_msg *msg = container_of(head, struct io_msg, tw);
- struct io_kiocb *req = cmd_to_io_kiocb(msg);
- struct io_ring_ctx *target_ctx = req->file->private_data;
- int ret = 0;
-
- if (current->flags & PF_EXITING) {
- ret = -EOWNERDEAD;
- } else {
- u32 flags = 0;
-
- if (msg->flags & IORING_MSG_RING_FLAGS_PASS)
- flags = msg->cqe_flags;
-
- /*
- * If the target ring is using IOPOLL mode, then we need to be
- * holding the uring_lock for posting completions. Other ring
- * types rely on the regular completion locking, which is
- * handled while posting.
- */
- if (target_ctx->flags & IORING_SETUP_IOPOLL)
- mutex_lock(&target_ctx->uring_lock);
- if (!io_post_aux_cqe(target_ctx, msg->user_data, msg->len, flags))
- ret = -EOVERFLOW;
- if (target_ctx->flags & IORING_SETUP_IOPOLL)
- mutex_unlock(&target_ctx->uring_lock);
+ bool is_cqe32 = target_ctx->flags & IORING_SETUP_CQE32;
+ size_t cqe_size = sizeof(struct io_overflow_cqe);
+ struct io_overflow_cqe *ocqe;
+
+ if (is_cqe32)
+ cqe_size += sizeof(struct io_uring_cqe);
+
+ ocqe = kmalloc(cqe_size, GFP_ATOMIC | __GFP_ACCOUNT);
+ if (!ocqe)
+ return NULL;
+
+ if (is_cqe32)
+ ocqe->cqe.big_cqe[0] = ocqe->cqe.big_cqe[1] = 0;
+
+ return ocqe;
+}
+
+/*
+ * Entered with the target uring_lock held, and will drop it before
+ * returning. Adds a previously allocated ocqe to the overflow list on
+ * the target, and marks it appropriately for flushing.
+ */
+static void io_msg_add_overflow(struct io_msg *msg,
+ struct io_ring_ctx *target_ctx,
+ struct io_overflow_cqe *ocqe, int ret,
+ u32 flags)
+ __releases(&target_ctx->completion_lock)
+{
+ if (list_empty(&target_ctx->cq_overflow_list)) {
+ set_bit(IO_CHECK_CQ_OVERFLOW_BIT, &target_ctx->check_cq);
+ atomic_or(IORING_SQ_TASKRUN, &target_ctx->rings->sq_flags);
}
- if (ret < 0)
- req_set_fail(req);
- io_req_queue_tw_complete(req, ret);
+ ocqe->cqe.user_data = msg->user_data;
+ ocqe->cqe.res = ret;
+ ocqe->cqe.flags = flags;
+ target_ctx->nr_overflow++;
+ list_add_tail(&ocqe->list, &target_ctx->cq_overflow_list);
+ spin_unlock(&target_ctx->completion_lock);
+ wake_up_state(target_ctx->submitter_task, TASK_INTERRUPTIBLE);
+}
+
+static int io_msg_fill_remote(struct io_msg *msg, unsigned int issue_flags,
+ struct io_ring_ctx *target_ctx, u32 flags)
+{
+ struct io_overflow_cqe *ocqe;
+
+ ocqe = io_alloc_overflow(target_ctx);
+ if (!ocqe)
+ return -ENOMEM;
+
+ spin_lock(&target_ctx->completion_lock);
+ io_msg_add_overflow(msg, target_ctx, ocqe, msg->len, flags);
+ return 0;
}
static int io_msg_ring_data(struct io_kiocb *req, unsigned int issue_flags)
@@ -135,12 +159,12 @@ static int io_msg_ring_data(struct io_kiocb *req, unsigned int issue_flags)
if (target_ctx->flags & IORING_SETUP_R_DISABLED)
return -EBADFD;
- if (io_msg_need_remote(target_ctx))
- return io_msg_exec_remote(req, io_msg_tw_complete);
-
if (msg->flags & IORING_MSG_RING_FLAGS_PASS)
flags = msg->cqe_flags;
+ if (io_msg_need_remote(target_ctx))
+ return io_msg_fill_remote(msg, issue_flags, target_ctx, flags);
+
ret = -EOVERFLOW;
if (target_ctx->flags & IORING_SETUP_IOPOLL) {
if (unlikely(io_double_lock_ctx(target_ctx, issue_flags)))
--
2.43.0
