> 在 2019年9月29日，22:54，Jens Axboe <axboe@xxxxxxxxx> 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@xxxxxxxxx>
>
> ---
>
> v2:
> - Improve naming
> - Improve async detection
> - Harden cases where we could miss req return
> - Add support for fsync/sync_file_range/recvmsg/sendmsg
>
> 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;
> }
>
> -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;
>
> --
> Jens Axboe
>
>
Hi Jens, are you sure this is version 2, why is it the same as v1?
Is Link [1] is the correct one?
Link: [1] http://git.kernel.dk/cgit/linux-block/patch/?id=39b0f9f8e295b98bbcfd448709fa298f5545e28c
--
BR, Jackie Liu
