io_uring: remove priority tw list optimisation

This optimisation has some built in assumptions that make it easy to
introduce bugs. It also does not have clear wins that make it worth keeping.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220622134028.2013417-2-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8bc6341..d21d0fc 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -986,44 +986,6 @@ static void ctx_flush_and_put(struct io_ring_ctx *ctx, bool *locked)
        percpu_ref_put(&ctx->refs);
 }
 
-static void handle_prev_tw_list(struct io_wq_work_node *node,
-                               struct io_ring_ctx **ctx, bool *uring_locked)
-{
-       if (*ctx && !*uring_locked)
-               spin_lock(&(*ctx)->completion_lock);
-
-       do {
-               struct io_wq_work_node *next = node->next;
-               struct io_kiocb *req = container_of(node, struct io_kiocb,
-                                                   io_task_work.node);
-
-               prefetch(container_of(next, struct io_kiocb, io_task_work.node));
-
-               if (req->ctx != *ctx) {
-                       if (unlikely(!*uring_locked && *ctx))
-                               io_cq_unlock_post(*ctx);
-
-                       ctx_flush_and_put(*ctx, uring_locked);
-                       *ctx = req->ctx;
-                       /* if not contended, grab and improve batching */
-                       *uring_locked = mutex_trylock(&(*ctx)->uring_lock);
-                       percpu_ref_get(&(*ctx)->refs);
-                       if (unlikely(!*uring_locked))
-                               io_cq_lock(*ctx);
-               }
-               if (likely(*uring_locked)) {
-                       req->io_task_work.func(req, uring_locked);
-               } else {
-                       req->cqe.flags = io_put_kbuf_comp(req);
-                       __io_req_complete_post(req);
-               }
-               node = next;
-       } while (node);
-
-       if (unlikely(!*uring_locked))
-               io_cq_unlock_post(*ctx);
-}
-
 static void handle_tw_list(struct io_wq_work_node *node,
                           struct io_ring_ctx **ctx, bool *locked)
 {
@@ -1054,27 +1016,20 @@ void tctx_task_work(struct callback_head *cb)
                                                  task_work);
 
        while (1) {
-               struct io_wq_work_node *node1, *node2;
+               struct io_wq_work_node *node;
 
                spin_lock_irq(&tctx->task_lock);
-               node1 = tctx->prio_task_list.first;
-               node2 = tctx->task_list.first;
+               node = tctx->task_list.first;
                INIT_WQ_LIST(&tctx->task_list);
-               INIT_WQ_LIST(&tctx->prio_task_list);
-               if (!node2 && !node1)
+               if (!node)
                        tctx->task_running = false;
                spin_unlock_irq(&tctx->task_lock);
-               if (!node2 && !node1)
+               if (!node)
                        break;
-
-               if (node1)
-                       handle_prev_tw_list(node1, &ctx, &uring_locked);
-               if (node2)
-                       handle_tw_list(node2, &ctx, &uring_locked);
+               handle_tw_list(node, &ctx, &uring_locked);
                cond_resched();
 
-               if (data_race(!tctx->task_list.first) &&
-                   data_race(!tctx->prio_task_list.first) && uring_locked)
+               if (data_race(!tctx->task_list.first) && uring_locked)
                        io_submit_flush_completions(ctx);
        }
 
@@ -1086,8 +1041,7 @@ void tctx_task_work(struct callback_head *cb)
 }
 
 static void __io_req_task_work_add(struct io_kiocb *req,
-                                  struct io_uring_task *tctx,
-                                  struct io_wq_work_list *list)
+                                  struct io_uring_task *tctx)
 {
        struct io_ring_ctx *ctx = req->ctx;
        struct io_wq_work_node *node;
@@ -1095,7 +1049,7 @@ static void __io_req_task_work_add(struct io_kiocb *req,
        bool running;
 
        spin_lock_irqsave(&tctx->task_lock, flags);
-       wq_list_add_tail(&req->io_task_work.node, list);
+       wq_list_add_tail(&req->io_task_work.node, &tctx->task_list);
        running = tctx->task_running;
        if (!running)
                tctx->task_running = true;
@@ -1113,7 +1067,8 @@ static void __io_req_task_work_add(struct io_kiocb *req,
 
        spin_lock_irqsave(&tctx->task_lock, flags);
        tctx->task_running = false;
-       node = wq_list_merge(&tctx->prio_task_list, &tctx->task_list);
+       node = tctx->task_list.first;
+       INIT_WQ_LIST(&tctx->task_list);
        spin_unlock_irqrestore(&tctx->task_lock, flags);
 
        while (node) {
@@ -1129,17 +1084,7 @@ void io_req_task_work_add(struct io_kiocb *req)
 {
        struct io_uring_task *tctx = req->task->io_uring;
 
-       __io_req_task_work_add(req, tctx, &tctx->task_list);
-}
-
-void io_req_task_prio_work_add(struct io_kiocb *req)
-{
-       struct io_uring_task *tctx = req->task->io_uring;
-
-       if (req->ctx->flags & IORING_SETUP_SQPOLL)
-               __io_req_task_work_add(req, tctx, &tctx->prio_task_list);
-       else
-               __io_req_task_work_add(req, tctx, &tctx->task_list);
+       __io_req_task_work_add(req, tctx);
 }
 
 static void io_req_tw_post(struct io_kiocb *req, bool *locked)

diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index f026d26..f77e4a5 100644 (file)
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -36,7 +36,6 @@ struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 bool io_is_uring_fops(struct file *file);
 bool io_alloc_async_data(struct io_kiocb *req);
 void io_req_task_work_add(struct io_kiocb *req);
-void io_req_task_prio_work_add(struct io_kiocb *req);
 void io_req_tw_post_queue(struct io_kiocb *req, s32 res, u32 cflags);
 void io_req_task_queue(struct io_kiocb *req);
 void io_queue_iowq(struct io_kiocb *req, bool *dont_use);

diff --git a/io_uring/rw.c b/io_uring/rw.c
index e07f267..ade3e23 100644 (file)
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -215,7 +215,7 @@ static void io_complete_rw(struct kiocb *kiocb, long res)
                return;
        io_req_set_res(req, res, 0);
        req->io_task_work.func = io_req_task_complete;
-       io_req_task_prio_work_add(req);
+       io_req_task_work_add(req);
 }
 
 static void io_complete_rw_iopoll(struct kiocb *kiocb, long res)

diff --git a/io_uring/tctx.c b/io_uring/tctx.c
index 9b30fb0..7a68ba9 100644 (file)
--- a/io_uring/tctx.c
+++ b/io_uring/tctx.c
@@ -88,7 +88,6 @@ __cold int io_uring_alloc_task_context(struct task_struct *task,
        task->io_uring = tctx;
        spin_lock_init(&tctx->task_lock);
        INIT_WQ_LIST(&tctx->task_list);
-       INIT_WQ_LIST(&tctx->prio_task_list);
        init_task_work(&tctx->task_work, tctx_task_work);
        return 0;
 }

diff --git a/io_uring/tctx.h b/io_uring/tctx.h
index dead0ed..c8566ea 100644 (file)
--- a/io_uring/tctx.h
+++ b/io_uring/tctx.h
@@ -22,7 +22,6 @@ struct io_uring_task {
                spinlock_t              task_lock;
                bool                    task_running;
                struct io_wq_work_list  task_list;
-               struct io_wq_work_list  prio_task_list;
                struct callback_head    task_work;
        } ____cacheline_aligned_in_smp;
 };