diff mbox series

io_uring: run dependent links inline if possible

Message ID e736649e-8360-ad69-8151-3cf3cf78b50f@kernel.dk (mailing list archive)
State New, archived
Headers show
Series io_uring: run dependent links inline if possible | expand

Commit Message

Jens Axboe Sept. 28, 2019, 11:23 p.m. UTC 
Currently any dependent link is executed from a new workqueue context,
which means that we'll be doing a context switch per link in the chain.
If we are running the completion of the current request from our async
workqueue and find that the next request is a link, then run it directly
from the workqueue context instead of forcing another switch.

This improves the performance of linked SQEs, and reduces the CPU
overhead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

2-3x speedup doing read-write links, where the read often ends up
blocking. Tested with examples/link-cp.c

Comments

Jackie Liu Sept. 29, 2019, 1:47 a.m. UTC | #1 
> 在 2019年9月29日，07:23，Jens Axboe <axboe@kernel.dk> 写道：
> 
> Currently any dependent link is executed from a new workqueue context,
> which means that we'll be doing a context switch per link in the chain.
> If we are running the completion of the current request from our async
> workqueue and find that the next request is a link, then run it directly
> from the workqueue context instead of forcing another switch.
> 
> This improves the performance of linked SQEs, and reduces the CPU
> overhead.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> 2-3x speedup doing read-write links, where the read often ends up
> blocking. Tested with examples/link-cp.c
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index aa8ac557493c..742d95563a54 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -667,7 +667,7 @@ static void __io_free_req(struct io_kiocb *req)
> 	kmem_cache_free(req_cachep, req);
> }
> 
> -static void io_req_link_next(struct io_kiocb *req)
> +struct io_kiocb *io_req_link_next(struct io_kiocb *req)
> {
> 	struct io_kiocb *nxt;
> 
> @@ -686,9 +686,19 @@ static void io_req_link_next(struct io_kiocb *req)
> 		}
> 
> 		nxt->flags |= REQ_F_LINK_DONE;
> +		/*
> +		 * If we're in async work, we can continue processing this,
> +		 * we can continue processing the chain in this context instead
> +		 * of having to queue up new async work.
> +		 */
> +		if (current_work())
> +			return nxt;
> 		INIT_WORK(&nxt->work, io_sq_wq_submit_work);
> 		io_queue_async_work(req->ctx, nxt);
> +		nxt = NULL;
> 	}
> +
> +	return nxt;
> }
> 
> /*
> @@ -707,8 +717,10 @@ static void io_fail_links(struct io_kiocb *req)
> 	}
> }
> 
> -static void io_free_req(struct io_kiocb *req)
> +static struct io_kiocb *io_free_req(struct io_kiocb *req)
> {
> +	struct io_kiocb *nxt = NULL;
> +
> 	/*
> 	 * If LINK is set, we have dependent requests in this chain. If we
> 	 * didn't fail this request, queue the first one up, moving any other
> @@ -719,16 +731,30 @@ static void io_free_req(struct io_kiocb *req)
> 		if (req->flags & REQ_F_FAIL_LINK)
> 			io_fail_links(req);
> 		else
> -			io_req_link_next(req);
> +			nxt = io_req_link_next(req);
> 	}
> 
> 	__io_free_req(req);
> +	return nxt;
> }
> 

LGTM, Reviewed-by: Jackie Liu <liuyun01@kylinos.cn>

The function io_free_req has been used not only for free req, but also for the task
of finding the next link entry. I think it is possible to change a name to avoid
confusion, of course, only personal opinion.

--
BR, Jackie Liu
Jens Axboe Sept. 29, 2019, 2:37 a.m. UTC | #2 
On 9/29/19 3:47 AM, Jackie Liu wrote:
> 
> 
>> 在 2019年9月29日，07:23，Jens Axboe <axboe@kernel.dk> 写道：
>>
>> Currently any dependent link is executed from a new workqueue context,
>> which means that we'll be doing a context switch per link in the chain.
>> If we are running the completion of the current request from our async
>> workqueue and find that the next request is a link, then run it directly
>> from the workqueue context instead of forcing another switch.
>>
>> This improves the performance of linked SQEs, and reduces the CPU
>> overhead.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> ---
>>
>> 2-3x speedup doing read-write links, where the read often ends up
>> blocking. Tested with examples/link-cp.c
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index aa8ac557493c..742d95563a54 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -667,7 +667,7 @@ static void __io_free_req(struct io_kiocb *req)
>> 	kmem_cache_free(req_cachep, req);
>> }
>>
>> -static void io_req_link_next(struct io_kiocb *req)
>> +struct io_kiocb *io_req_link_next(struct io_kiocb *req)
>> {
>> 	struct io_kiocb *nxt;
>>
>> @@ -686,9 +686,19 @@ static void io_req_link_next(struct io_kiocb *req)
>> 		}
>>
>> 		nxt->flags |= REQ_F_LINK_DONE;
>> +		/*
>> +		 * If we're in async work, we can continue processing this,
>> +		 * we can continue processing the chain in this context instead
>> +		 * of having to queue up new async work.
>> +		 */
>> +		if (current_work())
>> +			return nxt;
>> 		INIT_WORK(&nxt->work, io_sq_wq_submit_work);
>> 		io_queue_async_work(req->ctx, nxt);
>> +		nxt = NULL;
>> 	}
>> +
>> +	return nxt;
>> }
>>
>> /*
>> @@ -707,8 +717,10 @@ static void io_fail_links(struct io_kiocb *req)
>> 	}
>> }
>>
>> -static void io_free_req(struct io_kiocb *req)
>> +static struct io_kiocb *io_free_req(struct io_kiocb *req)
>> {
>> +	struct io_kiocb *nxt = NULL;
>> +
>> 	/*
>> 	 * If LINK is set, we have dependent requests in this chain. If we
>> 	 * didn't fail this request, queue the first one up, moving any other
>> @@ -719,16 +731,30 @@ static void io_free_req(struct io_kiocb *req)
>> 		if (req->flags & REQ_F_FAIL_LINK)
>> 			io_fail_links(req);
>> 		else
>> -			io_req_link_next(req);
>> +			nxt = io_req_link_next(req);
>> 	}
>>
>> 	__io_free_req(req);
>> +	return nxt;
>> }
>>
> 
> LGTM, Reviewed-by: Jackie Liu <liuyun01@kylinos.cn>
> 
> The function io_free_req has been used not only for free req, but also for the task
> of finding the next link entry. I think it is possible to change a name to avoid
> confusion, of course, only personal opinion.

That's a good point. I also changed how we handle the return of that, so there's
no confusion as to a caller getting a nxt request returned and not handling it.
See here:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-5.5/io_uring&id=778fd7a24868b329ff8da2784fd8ced5e35af78c

I'll send out a v2 that's the above, and your naming suggestion.
diff mbox series

Patch

diff --git a/fs/io_uring.c b/fs/io_uring.c
index aa8ac557493c..742d95563a54 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -667,7 +667,7 @@  static void __io_free_req(struct io_kiocb *req)
 	kmem_cache_free(req_cachep, req);
 }
 
-static void io_req_link_next(struct io_kiocb *req)
+struct io_kiocb *io_req_link_next(struct io_kiocb *req)
 {
 	struct io_kiocb *nxt;
 
@@ -686,9 +686,19 @@  static void io_req_link_next(struct io_kiocb *req)
 		}
 
 		nxt->flags |= REQ_F_LINK_DONE;
+		/*
+		 * If we're in async work, we can continue processing this,
+		 * we can continue processing the chain in this context instead
+		 * of having to queue up new async work.
+		 */
+		if (current_work())
+			return nxt;
 		INIT_WORK(&nxt->work, io_sq_wq_submit_work);
 		io_queue_async_work(req->ctx, nxt);
+		nxt = NULL;
 	}
+
+	return nxt;
 }
 
 /*
@@ -707,8 +717,10 @@  static void io_fail_links(struct io_kiocb *req)
 	}
 }
 
-static void io_free_req(struct io_kiocb *req)
+static struct io_kiocb *io_free_req(struct io_kiocb *req)
 {
+	struct io_kiocb *nxt = NULL;
+
 	/*
 	 * If LINK is set, we have dependent requests in this chain. If we
 	 * didn't fail this request, queue the first one up, moving any other
@@ -719,16 +731,30 @@  static void io_free_req(struct io_kiocb *req)
 		if (req->flags & REQ_F_FAIL_LINK)
 			io_fail_links(req);
 		else
-			io_req_link_next(req);
+			nxt = io_req_link_next(req);
 	}
 
 	__io_free_req(req);
+	return nxt;
 }
 
-static void io_put_req(struct io_kiocb *req)
+static struct io_kiocb *__io_put_req(struct io_kiocb *req)
 {
 	if (refcount_dec_and_test(&req->refs))
-		io_free_req(req);
+		return io_free_req(req);
+
+	return NULL;
+}
+
+static void io_put_req(struct io_kiocb *req)
+{
+	struct io_kiocb *nxt;
+
+	nxt = __io_put_req(req);
+	if (nxt) {
+		INIT_WORK(&nxt->work, io_sq_wq_submit_work);
+		io_queue_async_work(nxt->ctx, nxt);
+	}
 }
 
 static unsigned io_cqring_events(struct io_rings *rings)
@@ -934,7 +960,7 @@  static void kiocb_end_write(struct kiocb *kiocb)
 	}
 }
 
-static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
+static void io_complete_rw_common(struct kiocb *kiocb, long res)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
 
@@ -943,9 +969,24 @@  static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
 	if ((req->flags & REQ_F_LINK) && res != req->result)
 		req->flags |= REQ_F_FAIL_LINK;
 	io_cqring_add_event(req->ctx, req->user_data, res);
+}
+
+static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	io_complete_rw_common(kiocb, res);
 	io_put_req(req);
 }
 
+static struct io_kiocb *__io_complete_rw(struct kiocb *kiocb, long res)
+{
+	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
+
+	io_complete_rw_common(kiocb, res);
+	return __io_put_req(req);
+}
+
 static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 {
 	struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
@@ -1128,6 +1169,15 @@  static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
 	}
 }
 
+static void call_io_rw_done(struct kiocb *kiocb, ssize_t ret,
+			    struct io_kiocb **nxt, bool in_async)
+{
+	if (in_async && ret >= 0 && nxt && kiocb->ki_complete == io_complete_rw)
+		*nxt = __io_complete_rw(kiocb, ret);
+	else
+		io_rw_done(kiocb, ret);
+}
+
 static int io_import_fixed(struct io_ring_ctx *ctx, int rw,
 			   const struct io_uring_sqe *sqe,
 			   struct iov_iter *iter)
@@ -1344,7 +1394,7 @@  static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
 }
 
 static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
-		   bool force_nonblock)
+		   bool force_nonblock, struct io_kiocb **nxt)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -1391,7 +1441,7 @@  static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
 			ret2 = -EAGAIN;
 		/* Catch -EAGAIN return for forced non-blocking submission */
 		if (!force_nonblock || ret2 != -EAGAIN) {
-			io_rw_done(kiocb, ret2);
+			call_io_rw_done(kiocb, ret2, nxt, s->needs_lock);
 		} else {
 			/*
 			 * If ->needs_lock is true, we're already in async
@@ -1407,7 +1457,7 @@  static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
 }
 
 static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
-		    bool force_nonblock)
+		    bool force_nonblock, struct io_kiocb **nxt)
 {
 	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
 	struct kiocb *kiocb = &req->rw;
@@ -1465,7 +1515,7 @@  static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
 		else
 			ret2 = loop_rw_iter(WRITE, file, kiocb, &iter);
 		if (!force_nonblock || ret2 != -EAGAIN) {
-			io_rw_done(kiocb, ret2);
+			call_io_rw_done(kiocb, ret2, nxt, s->needs_lock);
 		} else {
 			/*
 			 * If ->needs_lock is true, we're already in async
@@ -1968,7 +2018,8 @@  static int io_req_defer(struct io_ring_ctx *ctx, struct io_kiocb *req,
 }
 
 static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
-			   const struct sqe_submit *s, bool force_nonblock)
+			   const struct sqe_submit *s, bool force_nonblock,
+			   struct io_kiocb **nxt)
 {
 	int ret, opcode;
 
@@ -1985,18 +2036,18 @@  static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_READV:
 		if (unlikely(s->sqe->buf_index))
 			return -EINVAL;
-		ret = io_read(req, s, force_nonblock);
+		ret = io_read(req, s, force_nonblock, nxt);
 		break;
 	case IORING_OP_WRITEV:
 		if (unlikely(s->sqe->buf_index))
 			return -EINVAL;
-		ret = io_write(req, s, force_nonblock);
+		ret = io_write(req, s, force_nonblock, nxt);
 		break;
 	case IORING_OP_READ_FIXED:
-		ret = io_read(req, s, force_nonblock);
+		ret = io_read(req, s, force_nonblock, nxt);
 		break;
 	case IORING_OP_WRITE_FIXED:
-		ret = io_write(req, s, force_nonblock);
+		ret = io_write(req, s, force_nonblock, nxt);
 		break;
 	case IORING_OP_FSYNC:
 		ret = io_fsync(req, s->sqe, force_nonblock);
@@ -2081,6 +2132,7 @@  static void io_sq_wq_submit_work(struct work_struct *work)
 		struct sqe_submit *s = &req->submit;
 		const struct io_uring_sqe *sqe = s->sqe;
 		unsigned int flags = req->flags;
+		struct io_kiocb *nxt = NULL;
 
 		/* Ensure we clear previously set non-block flag */
 		req->rw.ki_flags &= ~IOCB_NOWAIT;
@@ -2101,7 +2153,7 @@  static void io_sq_wq_submit_work(struct work_struct *work)
 			s->has_user = cur_mm != NULL;
 			s->needs_lock = true;
 			do {
-				ret = __io_submit_sqe(ctx, req, s, false);
+				ret = __io_submit_sqe(ctx, req, s, false, &nxt);
 				/*
 				 * We can get EAGAIN for polled IO even though
 				 * we're forcing a sync submission from here,
@@ -2125,6 +2177,12 @@  static void io_sq_wq_submit_work(struct work_struct *work)
 		/* async context always use a copy of the sqe */
 		kfree(sqe);
 
+		/* if a dependent link is ready, do that as the next one */
+		if (!ret && nxt) {
+			req = nxt;
+			continue;
+		}
+
 		/* req from defer and link list needn't decrease async cnt */
 		if (flags & (REQ_F_IO_DRAINED | REQ_F_LINK_DONE))
 			goto out;
@@ -2271,7 +2329,7 @@  static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 {
 	int ret;
 
-	ret = __io_submit_sqe(ctx, req, s, force_nonblock);
+	ret = __io_submit_sqe(ctx, req, s, force_nonblock, NULL);
 	if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {
 		struct io_uring_sqe *sqe_copy;