Re: [PATCH v2 3/4] io_uring: don't spinlock when not posting CQEs

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/11/10 下午11:49, Pavel Begunkov 写道:
> When no of queued for the batch completion requests need to post an CQE,
> see IOSQE_CQE_SKIP_SUCCESS, avoid grabbing ->completion_lock and other
> commit/post.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>   fs/io_uring.c | 26 +++++++++++++++++---------
>   1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 22572cfd6864..0c0ea3bbb50a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -321,6 +321,7 @@ struct io_submit_state {
>   
>   	bool			plug_started;
>   	bool			need_plug;
> +	bool			flush_cqes;
>   	unsigned short		submit_nr;
>   	struct blk_plug		plug;
>   };
> @@ -1525,8 +1526,11 @@ static void io_prep_async_link(struct io_kiocb *req)
>   
>   static inline void io_req_add_compl_list(struct io_kiocb *req)
>   {
> +	struct io_ring_ctx *ctx = req->ctx;
>   	struct io_submit_state *state = &req->ctx->submit_state;
>   
> +	if (!(req->flags & REQ_F_CQE_SKIP))
> +		ctx->submit_state.flush_cqes = true;
Should we init it to false in submit_state_start()?
>   	wq_list_add_tail(&req->comp_list, &state->compl_reqs);
>   }
>   
> @@ -2386,18 +2390,22 @@ 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;
>   
> -	spin_lock(&ctx->completion_lock);
> -	wq_list_for_each(node, prev, &state->compl_reqs) {
> -		struct io_kiocb *req = container_of(node, struct io_kiocb,
> +	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(ctx, req->user_data, req->result,
> -				      req->cflags);
> +			if (!(req->flags & REQ_F_CQE_SKIP))
> +				__io_fill_cqe(ctx, req->user_data, req->result,
> +					      req->cflags);
> +		}
> +
> +		io_commit_cqring(ctx);
> +		spin_unlock(&ctx->completion_lock);
> +		io_cqring_ev_posted(ctx);
> +		state->flush_cqes = false;
>   	}
> -	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);
>