io_uring: run dependent links inline if possible

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.

Reviewed-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c11c4157a4c22c6c0d718749fd0e68beefda409b..5db0854fec7417f48092d86d97ed7ec369943cbc 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -666,7 +666,7 @@ 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)
+static void io_req_link_next(struct io_kiocb *req, struct io_kiocb **nxtptr)
 {
        struct io_kiocb *nxt;
 
@@ -685,8 +685,16 @@ static void io_req_link_next(struct io_kiocb *req)
                }
 
                nxt->flags |= REQ_F_LINK_DONE;
-               INIT_WORK(&nxt->work, io_sq_wq_submit_work);
-               io_queue_async_work(req->ctx, nxt);
+               /*
+                * If we're in async work, we can continue processing the chain
+                * in this context instead of having to queue up new async work.
+                */
+               if (nxtptr && current_work()) {
+                       *nxtptr = nxt;
+               } else {
+                       INIT_WORK(&nxt->work, io_sq_wq_submit_work);
+                       io_queue_async_work(req->ctx, nxt);
+               }
        }
 }
 
@@ -706,7 +714,7 @@ static void io_fail_links(struct io_kiocb *req)
        }
 }
 
-static void io_free_req(struct io_kiocb *req)
+static void io_free_req(struct io_kiocb *req, struct io_kiocb **nxt)
 {
        /*
         * If LINK is set, we have dependent requests in this chain. If we
@@ -718,16 +726,39 @@ 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);
+                       io_req_link_next(req, nxt);
        }
 
        __io_free_req(req);
 }
 
-static void io_put_req(struct io_kiocb *req)
+/*
+ * Drop reference to request, return next in chain (if there is one) if this
+ * was the last reference to this request.
+ */
+static struct io_kiocb *io_put_req_find_next(struct io_kiocb *req)
 {
+       struct io_kiocb *nxt = NULL;
+
        if (refcount_dec_and_test(&req->refs))
-               io_free_req(req);
+               io_free_req(req, &nxt);
+
+       return nxt;
+}
+
+static void io_put_req(struct io_kiocb *req, struct io_kiocb **nxtptr)
+{
+       struct io_kiocb *nxt;
+
+       nxt = io_put_req_find_next(req);
+       if (nxt) {
+               if (nxtptr) {
+                       *nxtptr = nxt;
+               } else {
+                       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)
@@ -775,7 +806,7 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
                                if (to_free == ARRAY_SIZE(reqs))
                                        io_free_req_many(ctx, reqs, &to_free);
                        } else {
-                               io_free_req(req);
+                               io_free_req(req, NULL);
                        }
                }
        }
@@ -947,7 +978,7 @@ static void kiocb_end_write(struct io_kiocb *req)
        file_end_write(req->file);
 }
 
-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);
 
@@ -957,7 +988,22 @@ 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);
-       io_put_req(req);
+}
+
+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, NULL);
+}
+
+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_find_next(req);
 }
 
 static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
@@ -1153,6 +1199,15 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
        }
 }
 
+static void kiocb_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)
@@ -1369,7 +1424,7 @@ 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)
+                  struct io_kiocb **nxt, bool force_nonblock)
 {
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw;
@@ -1418,7 +1473,7 @@ 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);
+                       kiocb_done(kiocb, ret2, nxt, s->needs_lock);
                } else {
                        /*
                         * If ->needs_lock is true, we're already in async
@@ -1434,7 +1489,7 @@ 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)
+                   struct io_kiocb **nxt, bool force_nonblock)
 {
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct kiocb *kiocb = &req->rw;
@@ -1492,7 +1547,7 @@ 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);
+                       kiocb_done(kiocb, ret2, nxt, s->needs_lock);
                } else {
                        /*
                         * If ->needs_lock is true, we're already in async
@@ -1520,7 +1575,7 @@ static int io_nop(struct io_kiocb *req, u64 user_data)
                return -EINVAL;
 
        io_cqring_add_event(ctx, user_data, err);
-       io_put_req(req);
+       io_put_req(req, NULL);
        return 0;
 }
 
@@ -1540,7 +1595,7 @@ static int io_prep_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 }
 
 static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-                   bool force_nonblock)
+                   struct io_kiocb **nxt, bool force_nonblock)
 {
        loff_t sqe_off = READ_ONCE(sqe->off);
        loff_t sqe_len = READ_ONCE(sqe->len);
@@ -1567,7 +1622,7 @@ static int io_fsync(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
-       io_put_req(req);
+       io_put_req(req, nxt);
        return 0;
 }
 
@@ -1589,6 +1644,7 @@ static int io_prep_sfr(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 static int io_sync_file_range(struct io_kiocb *req,
                              const struct io_uring_sqe *sqe,
+                             struct io_kiocb **nxt,
                              bool force_nonblock)
 {
        loff_t sqe_off;
@@ -1613,13 +1669,13 @@ static int io_sync_file_range(struct io_kiocb *req,
        if (ret < 0 && (req->flags & REQ_F_LINK))
                req->flags |= REQ_F_FAIL_LINK;
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
-       io_put_req(req);
+       io_put_req(req, nxt);
        return 0;
 }
 
 #if defined(CONFIG_NET)
 static int io_send_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-                          bool force_nonblock,
+                          struct io_kiocb **nxt, bool force_nonblock,
                   long (*fn)(struct socket *, struct user_msghdr __user *,
                                unsigned int))
 {
@@ -1649,26 +1705,28 @@ static int io_send_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        }
 
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
-       io_put_req(req);
+       io_put_req(req, nxt);
        return 0;
 }
 #endif
 
 static int io_sendmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-                     bool force_nonblock)
+                     struct io_kiocb **nxt, bool force_nonblock)
 {
 #if defined(CONFIG_NET)
-       return io_send_recvmsg(req, sqe, force_nonblock, __sys_sendmsg_sock);
+       return io_send_recvmsg(req, sqe, nxt, force_nonblock,
+                               __sys_sendmsg_sock);
 #else
        return -EOPNOTSUPP;
 #endif
 }
 
 static int io_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
-                     bool force_nonblock)
+                     struct io_kiocb **nxt, bool force_nonblock)
 {
 #if defined(CONFIG_NET)
-       return io_send_recvmsg(req, sqe, force_nonblock, __sys_recvmsg_sock);
+       return io_send_recvmsg(req, sqe, nxt, force_nonblock,
+                               __sys_recvmsg_sock);
 #else
        return -EOPNOTSUPP;
 #endif
@@ -1728,7 +1786,7 @@ static int io_poll_remove(struct io_kiocb *req, const struct io_uring_sqe *sqe)
        spin_unlock_irq(&ctx->completion_lock);
 
        io_cqring_add_event(req->ctx, sqe->user_data, ret);
-       io_put_req(req);
+       io_put_req(req, NULL);
        return 0;
 }
 
@@ -1769,7 +1827,7 @@ static void io_poll_complete_work(struct work_struct *work)
        spin_unlock_irq(&ctx->completion_lock);
 
        io_cqring_ev_posted(ctx);
-       io_put_req(req);
+       io_put_req(req, NULL);
 }
 
 static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
@@ -1794,7 +1852,7 @@ static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                spin_unlock_irqrestore(&ctx->completion_lock, flags);
 
                io_cqring_ev_posted(ctx);
-               io_put_req(req);
+               io_put_req(req, NULL);
        } else {
                io_queue_async_work(ctx, req);
        }
@@ -1886,7 +1944,7 @@ static int io_poll_add(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
        if (mask) {
                io_cqring_ev_posted(ctx);
-               io_put_req(req);
+               io_put_req(req, NULL);
        }
        return ipt.error;
 }
@@ -1919,7 +1977,7 @@ static enum hrtimer_restart io_timeout_fn(struct hrtimer *timer)
 
        io_cqring_ev_posted(ctx);
 
-       io_put_req(req);
+       io_put_req(req, NULL);
        return HRTIMER_NORESTART;
 }
 
@@ -2028,7 +2086,8 @@ 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, struct io_kiocb **nxt,
+                          bool force_nonblock)
 {
        int ret, opcode;
 
@@ -2045,21 +2104,21 @@ 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, nxt, force_nonblock);
                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, nxt, force_nonblock);
                break;
        case IORING_OP_READ_FIXED:
-               ret = io_read(req, s, force_nonblock);
+               ret = io_read(req, s, nxt, force_nonblock);
                break;
        case IORING_OP_WRITE_FIXED:
-               ret = io_write(req, s, force_nonblock);
+               ret = io_write(req, s, nxt, force_nonblock);
                break;
        case IORING_OP_FSYNC:
-               ret = io_fsync(req, s->sqe, force_nonblock);
+               ret = io_fsync(req, s->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_POLL_ADD:
                ret = io_poll_add(req, s->sqe);
@@ -2068,13 +2127,13 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
                ret = io_poll_remove(req, s->sqe);
                break;
        case IORING_OP_SYNC_FILE_RANGE:
-               ret = io_sync_file_range(req, s->sqe, force_nonblock);
+               ret = io_sync_file_range(req, s->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_SENDMSG:
-               ret = io_sendmsg(req, s->sqe, force_nonblock);
+               ret = io_sendmsg(req, s->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_RECVMSG:
-               ret = io_recvmsg(req, s->sqe, force_nonblock);
+               ret = io_recvmsg(req, s->sqe, nxt, force_nonblock);
                break;
        case IORING_OP_TIMEOUT:
                ret = io_timeout(req, s->sqe);
@@ -2141,6 +2200,7 @@ restart:
                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;
@@ -2161,7 +2221,7 @@ restart:
                        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, &nxt, false);
                                /*
                                 * We can get EAGAIN for polled IO even though
                                 * we're forcing a sync submission from here,
@@ -2175,16 +2235,22 @@ restart:
                }
 
                /* drop submission reference */
-               io_put_req(req);
+               io_put_req(req, NULL);
 
                if (ret) {
                        io_cqring_add_event(ctx, sqe->user_data, ret);
-                       io_put_req(req);
+                       io_put_req(req, NULL);
                }
 
                /* 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;
@@ -2331,7 +2397,7 @@ static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 {
        int ret;
 
-       ret = __io_submit_sqe(ctx, req, s, true);
+       ret = __io_submit_sqe(ctx, req, s, NULL, true);
 
        /*
         * We async punt it if the file wasn't marked NOWAIT, or if the file
@@ -2364,14 +2430,14 @@ static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
        }
 
        /* drop submission reference */
-       io_put_req(req);
+       io_put_req(req, NULL);
 
        /* and drop final reference, if we failed */
        if (ret) {
                io_cqring_add_event(ctx, req->user_data, ret);
                if (req->flags & REQ_F_LINK)
                        req->flags |= REQ_F_FAIL_LINK;
-               io_put_req(req);
+               io_put_req(req, NULL);
        }
 
        return ret;
@@ -2385,7 +2451,7 @@ static int io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
        ret = io_req_defer(ctx, req, s->sqe);
        if (ret) {
                if (ret != -EIOCBQUEUED) {
-                       io_free_req(req);
+                       io_free_req(req, NULL);
                        io_cqring_add_event(ctx, s->sqe->user_data, ret);
                }
                return 0;
@@ -2412,7 +2478,7 @@ static int io_queue_link_head(struct io_ring_ctx *ctx, struct io_kiocb *req,
        ret = io_req_defer(ctx, req, s->sqe);
        if (ret) {
                if (ret != -EIOCBQUEUED) {
-                       io_free_req(req);
+                       io_free_req(req, NULL);
                        __io_free_req(shadow);
                        io_cqring_add_event(ctx, s->sqe->user_data, ret);
                        return 0;
@@ -2460,7 +2526,7 @@ static void io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
        ret = io_req_set_file(ctx, s, state, req);
        if (unlikely(ret)) {
 err_req:
-               io_free_req(req);
+               io_free_req(req, NULL);
 err:
                io_cqring_add_event(ctx, s->sqe->user_data, ret);
                return;