[PATCH for-next 5/7] io_uring: remove ->flush_cqes optimisation

Pavel Begunkov
2022-06-19T11:26:50Z

It's not clear how widely used IOSQE_CQE_SKIP_SUCCESS is, and how often
->flush_cqes flag prevents from completion being flushed. Sometimes it's
high level of concurrency that enables it at least for one CQE, but
sometimes it doesn't save much because nobody waiting on the CQ.

Remove ->flush_cqes flag and the optimisation, it should benefit the
normal use case. Note, that there is no spurious eventfd problem with
that as checks for spuriousness were incorporated into
io_eventfd_signal().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
io_uring/io_uring.c | 23 ++++++++++-------------
io_uring/io_uring.h | 2 --
2 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 0875cc649e23..57aef092ef38 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1253,22 +1253,19 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
struct io_wq_work_node *node, *prev;
struct io_submit_state *state = &ctx->submit_state;

- if (state->flush_cqes) {
- spin_lock(&ctx->completion_lock);
- wq_list_for_each(node, prev, &state->compl_reqs) {
- struct io_kiocb *req = container_of(node, struct io_kiocb,
- comp_list);
-
- if (!(req->flags & REQ_F_CQE_SKIP))
- __io_fill_cqe_req(ctx, req);
- }
+ spin_lock(&ctx->completion_lock);
+ wq_list_for_each(node, prev, &state->compl_reqs) {
+ struct io_kiocb *req = container_of(node, struct io_kiocb,
+ comp_list);

- io_commit_cqring(ctx);
- spin_unlock(&ctx->completion_lock);
- io_cqring_ev_posted(ctx);
- state->flush_cqes = false;
+ if (!(req->flags & REQ_F_CQE_SKIP))
+ __io_fill_cqe_req(ctx, req);
}

+ io_commit_cqring(ctx);
+ spin_unlock(&ctx->completion_lock);
+ io_cqring_ev_posted(ctx);
+
io_free_batch_list(ctx, state->compl_reqs.first);
INIT_WQ_LIST(&state->compl_reqs);
}
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 906749fa3415..7feef8c36db7 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -232,8 +232,6 @@ static inline void io_req_complete_defer(struct io_kiocb *req)

lockdep_assert_held(&req->ctx->uring_lock);

- if (!(req->flags & REQ_F_CQE_SKIP))
- state->flush_cqes = true;
wq_list_add_tail(&req->comp_list, &state->compl_reqs);
}

--
2.36.1