Re: [PATCH 5/5] io_uring: leverage completion cache for poll requests

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

在 2021/9/18 上午3:38, Hao Xu 写道:
> Leverage completion cache to handle completions of poll requests in a
> batch.
> Good thing is we save compl_nr - 1 completion_lock and
> io_cqring_ev_posted.
> Bad thing is compl_nr extra ifs in flush_completion.
> 
> Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Sorry, please ignore this one, didn't notice it failed to pass
poll-mshot-update test
> ---
>   fs/io_uring.c | 64 +++++++++++++++++++++++++++++++++++++++------------
>   1 file changed, 49 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b1d6c3a1d3cd..0f72cb0bf79a 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -1099,6 +1099,8 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
>   				 unsigned int issue_flags, u32 slot_index);
>   static enum hrtimer_restart io_link_timeout_fn(struct hrtimer *timer);
>   
> +static bool io_complete_poll(struct io_kiocb *req);
> +
>   static struct kmem_cache *req_cachep;
>   
>   static const struct file_operations io_uring_fops;
> @@ -2333,6 +2335,11 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
>   	for (i = 0; i < nr; i++) {
>   		struct io_kiocb *req = state->compl_reqs[i];
>   
> +		if (req->opcode == IORING_OP_POLL_ADD) {
> +			if (!io_complete_poll(req))
> +				state->compl_reqs[i] = NULL;
> +			continue;
> +		}
>   		__io_cqring_fill_event(ctx, req->user_data, req->result,
>   					req->compl.cflags);
>   	}
> @@ -2344,7 +2351,7 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
>   	for (i = 0; i < nr; i++) {
>   		struct io_kiocb *req = state->compl_reqs[i];
>   
> -		if (req_ref_put_and_test(req))
> +		if (req && req_ref_put_and_test(req))
>   			io_req_free_batch(&rb, req, &ctx->submit_state);
>   	}
>   
> @@ -5360,6 +5367,23 @@ static inline void io_poll_complete(struct io_kiocb *req, __poll_t mask)
>   	return;
>   }
>   
> +static bool io_complete_poll(struct io_kiocb *req)
> +{
> +	bool done;
> +
> +	done = __io_poll_complete(req, req->result);
> +	if (done) {
> +		io_poll_remove_double(req);
> +		hash_del(&req->hash_node);
> +		req->poll.done = true;
> +	} else {
> +		req->result = 0;
> +		add_wait_queue(req->poll.head, &req->poll.wait);
> +	}
> +
> +	return done;
> +}
> +
>   static void io_poll_task_func(struct io_kiocb *req, bool *locked)
>   {
>   	struct io_ring_ctx *ctx = req->ctx;
> @@ -5367,18 +5391,10 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
>   
>   	if (io_poll_rewait(req, &req->poll)) {
>   		spin_unlock(&ctx->completion_lock);
> -	} else {
> +	} else if (!*locked) {
>   		bool done;
>   
> -		done = __io_poll_complete(req, req->result);
> -		if (done) {
> -			io_poll_remove_double(req);
> -			hash_del(&req->hash_node);
> -			req->poll.done = true;
> -		} else {
> -			req->result = 0;
> -			add_wait_queue(req->poll.head, &req->poll.wait);
> -		}
> +		done = io_complete_poll(req);
>   		io_commit_cqring(ctx);
>   		spin_unlock(&ctx->completion_lock);
>   		io_cqring_ev_posted(ctx);
> @@ -5388,6 +5404,13 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
>   			if (nxt)
>   				io_req_task_submit(nxt, locked);
>   		}
> +	} else {
> +		struct io_submit_state *state = &ctx->submit_state;
> +
> +		spin_unlock(&ctx->completion_lock);
> +		state->compl_reqs[state->compl_nr++] = req;
> +		if (state->compl_nr == ARRAY_SIZE(state->compl_reqs))
> +			io_submit_flush_completions(ctx);
>   	}
>   }
>   
> @@ -5833,6 +5856,7 @@ static int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
>   	struct io_ring_ctx *ctx = req->ctx;
>   	struct io_poll_table ipt;
>   	__poll_t mask;
> +	bool locked = current == req->task;
>   
>   	ipt.pt._qproc = io_poll_queue_proc;
>   
> @@ -5841,14 +5865,24 @@ static int io_poll_add(struct io_kiocb *req, unsigned int issue_flags)
>   
>   	if (mask) { /* no async, we'd stolen it */
>   		ipt.error = 0;
> -		io_poll_complete(req, mask);
> +		if (!locked)
> +			io_poll_complete(req, mask);
>   	}
>   	spin_unlock(&ctx->completion_lock);
>   
>   	if (mask) {
> -		io_cqring_ev_posted(ctx);
> -		if (poll->events & EPOLLONESHOT)
> -			io_put_req(req);
> +		if (!locked) {
> +			io_cqring_ev_posted(ctx);
> +			if (poll->events & EPOLLONESHOT)
> +				io_put_req(req);
> +		} else {
> +			struct io_submit_state *state = &ctx->submit_state;
> +
> +			req->result = mask;
> +			state->compl_reqs[state->compl_nr++] = req;
> +			if (state->compl_nr == ARRAY_SIZE(state->compl_reqs))
> +				io_submit_flush_completions(ctx);
> +		}
>   	}
>   	return ipt.error;
>   }
>