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

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

在 2021/9/11 下午9:52, 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 | 24 +++++++++++++++---------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 172c857e8b3f..8983a5a6851a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -317,6 +317,7 @@ struct io_submit_state {
>   
>   	bool			plug_started;
>   	bool			need_plug;
> +	bool			flush_cqes;
>   
>   	/*
>   	 * Batch completion logic
> @@ -1858,6 +1859,8 @@ static void io_req_complete_state(struct io_kiocb *req, long res,
>   	req->result = res;
>   	req->compl.cflags = cflags;
>   	req->flags |= REQ_F_COMPLETE_INLINE;
> +	if (!(req->flags & IOSQE_CQE_SKIP_SUCCESS))
Haven't look into this patchset deeply, but this looks
like should be REQ_F_CQE_SKIP ?
> +		req->ctx->submit_state.flush_cqes = true;
>   }
>   
>   static inline void __io_req_complete(struct io_kiocb *req, unsigned issue_flags,
> @@ -2354,17 +2357,19 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
>   	int i, nr = state->compl_nr;
>   	struct req_batch rb;
>   
> -	spin_lock(&ctx->completion_lock);
> -	for (i = 0; i < nr; i++) {
> -		struct io_kiocb *req = state->compl_reqs[i];
> +	if (state->flush_cqes) {
> +		spin_lock(&ctx->completion_lock);
> +		for (i = 0; i < nr; i++) {
> +			struct io_kiocb *req = state->compl_reqs[i];
>   
> -		if (!(req->flags & REQ_F_CQE_SKIP))
> -			__io_fill_cqe(ctx, req->user_data, req->result,
> -				      req->compl.cflags);
> +			if (!(req->flags & REQ_F_CQE_SKIP))
> +				__io_fill_cqe(ctx, req->user_data, req->result,
> +					      req->compl.cflags);
> +		}
> +		io_commit_cqring(ctx);
> +		spin_unlock(&ctx->completion_lock);
> +		io_cqring_ev_posted(ctx);
>   	}
> -	io_commit_cqring(ctx);
> -	spin_unlock(&ctx->completion_lock);
> -	io_cqring_ev_posted(ctx);
>   
>   	io_init_req_batch(&rb);
>   	for (i = 0; i < nr; i++) {
> @@ -2376,6 +2381,7 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
>   
>   	io_req_free_batch_finish(ctx, &rb);
>   	state->compl_nr = 0;
> +	state->flush_cqes = false;
>   }
>   
>   /*
>