From 9ca9fb24d5febccea354089c41f96a8ad0d853f8 Mon Sep 17 00:00:00 2001 From: Pavel Begunkov Date: Thu, 16 Jun 2022 10:22:12 +0100 Subject: [PATCH] io_uring: mutex locked poll hashing Currently we do two extra spin lock/unlock pairs to add a poll/apoll request to the cancellation hash table and remove it from there. On the submission side we often already hold ->uring_lock and tw completion is likely to hold it as well. Add a second cancellation hash table protected by ->uring_lock. In concerns for latency because of a need to have the mutex locked on the completion side, use the new table only in following cases: 1) IORING_SETUP_SINGLE_ISSUER: only one task grabs uring_lock, so there is little to no contention and so the main tw hander will almost always end up grabbing it before calling callbacks. 2) IORING_SETUP_SQPOLL: same as with single issuer, only one task is a major user of ->uring_lock. 3) apoll: we normally grab the lock on the completion side anyway to execute the request, so it's free. Signed-off-by: Pavel Begunkov Link: https://lore.kernel.org/r/1bbad9c78c454b7b92f100bbf46730a37df7194f.1655371007.git.asml.silence@gmail.com Reviewed-by: Hao Xu Signed-off-by: Jens Axboe --- io_uring/io_uring.c | 9 +++- io_uring/io_uring_types.h | 4 ++ io_uring/poll.c | 117 +++++++++++++++++++++++++++++++++++++--------- 3 files changed, 108 insertions(+), 22 deletions(-) diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 0b3851a..eeda167 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -275,6 +275,8 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) hash_bits = clamp(hash_bits, 1, 8); if (io_alloc_hash_table(&ctx->cancel_table, hash_bits)) goto err; + if (io_alloc_hash_table(&ctx->cancel_table_locked, hash_bits)) + goto err; ctx->dummy_ubuf = kzalloc(sizeof(*ctx->dummy_ubuf), GFP_KERNEL); if (!ctx->dummy_ubuf) @@ -317,6 +319,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p) err: kfree(ctx->dummy_ubuf); kfree(ctx->cancel_table.hbs); + kfree(ctx->cancel_table_locked.hbs); kfree(ctx->io_bl); xa_destroy(&ctx->io_bl_xa); kfree(ctx); @@ -2493,6 +2496,7 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx) if (ctx->hash_map) io_wq_put_hash(ctx->hash_map); kfree(ctx->cancel_table.hbs); + kfree(ctx->cancel_table_locked.hbs); kfree(ctx->dummy_ubuf); kfree(ctx->io_bl); xa_destroy(&ctx->io_bl_xa); @@ -2654,12 +2658,13 @@ static __cold void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx) __io_cqring_overflow_flush(ctx, true); xa_for_each(&ctx->personalities, index, creds) io_unregister_personality(ctx, index); + if (ctx->rings) + io_poll_remove_all(ctx, NULL, true); mutex_unlock(&ctx->uring_lock); /* failed during ring init, it couldn't have issued any requests */ if (ctx->rings) { io_kill_timeouts(ctx, NULL, true); - io_poll_remove_all(ctx, NULL, true); /* if we failed setting up the ctx, we might not have any rings */ io_iopoll_try_reap_events(ctx); } @@ -2784,7 +2789,9 @@ static __cold void io_uring_try_cancel_requests(struct io_ring_ctx *ctx, } ret |= io_cancel_defer_files(ctx, task, cancel_all); + mutex_lock(&ctx->uring_lock); ret |= io_poll_remove_all(ctx, task, cancel_all); + mutex_unlock(&ctx->uring_lock); ret |= io_kill_timeouts(ctx, task, cancel_all); if (task) ret |= io_run_task_work(); diff --git a/io_uring/io_uring_types.h b/io_uring/io_uring_types.h index d3b9bde..65ac7cd 100644 --- a/io_uring/io_uring_types.h +++ b/io_uring/io_uring_types.h @@ -191,6 +191,7 @@ struct io_ring_ctx { struct xarray io_bl_xa; struct list_head io_buffers_cache; + struct io_hash_table cancel_table_locked; struct list_head cq_overflow_list; struct list_head apoll_cache; struct xarray personalities; @@ -323,6 +324,7 @@ enum { REQ_F_CQE32_INIT_BIT, REQ_F_APOLL_MULTISHOT_BIT, REQ_F_CLEAR_POLLIN_BIT, + REQ_F_HASH_LOCKED_BIT, /* keep async read/write and isreg together and in order */ REQ_F_SUPPORT_NOWAIT_BIT, REQ_F_ISREG_BIT, @@ -393,6 +395,8 @@ enum { REQ_F_CQE32_INIT = BIT(REQ_F_CQE32_INIT_BIT), /* recvmsg special flag, clear EPOLLIN */ REQ_F_CLEAR_POLLIN = BIT(REQ_F_CLEAR_POLLIN_BIT), + /* hashed into ->cancel_hash_locked, protected by ->uring_lock */ + REQ_F_HASH_LOCKED = BIT(REQ_F_HASH_LOCKED_BIT), }; typedef void (*io_req_tw_func_t)(struct io_kiocb *req, bool *locked); diff --git a/io_uring/poll.c b/io_uring/poll.c index c4edf87..9ae2982 100644 --- a/io_uring/poll.c +++ b/io_uring/poll.c @@ -93,6 +93,32 @@ static void io_poll_req_delete(struct io_kiocb *req, struct io_ring_ctx *ctx) spin_unlock(lock); } +static void io_poll_req_insert_locked(struct io_kiocb *req) +{ + struct io_hash_table *table = &req->ctx->cancel_table_locked; + u32 index = hash_long(req->cqe.user_data, table->hash_bits); + + hlist_add_head(&req->hash_node, &table->hbs[index].list); +} + +static void io_poll_tw_hash_eject(struct io_kiocb *req, bool *locked) +{ + struct io_ring_ctx *ctx = req->ctx; + + if (req->flags & REQ_F_HASH_LOCKED) { + /* + * ->cancel_table_locked is protected by ->uring_lock in + * contrast to per bucket spinlocks. Likely, tctx_task_work() + * already grabbed the mutex for us, but there is a chance it + * failed. + */ + io_tw_lock(ctx, locked); + hash_del(&req->hash_node); + } else { + io_poll_req_delete(req, ctx); + } +} + static void io_init_poll_iocb(struct io_poll *poll, __poll_t events, wait_queue_func_t wake_func) { @@ -217,7 +243,6 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked) static void io_poll_task_func(struct io_kiocb *req, bool *locked) { - struct io_ring_ctx *ctx = req->ctx; int ret; ret = io_poll_check_events(req, locked); @@ -234,7 +259,8 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked) } io_poll_remove_entries(req); - io_poll_req_delete(req, ctx); + io_poll_tw_hash_eject(req, locked); + io_req_set_res(req, req->cqe.res, 0); io_req_task_complete(req, locked); } @@ -248,7 +274,7 @@ static void io_apoll_task_func(struct io_kiocb *req, bool *locked) return; io_poll_remove_entries(req); - io_poll_req_delete(req, req->ctx); + io_poll_tw_hash_eject(req, locked); if (!ret) io_req_task_submit(req, locked); @@ -444,7 +470,10 @@ static int __io_arm_poll_handler(struct io_kiocb *req, return 0; } - io_poll_req_insert(req); + if (req->flags & REQ_F_HASH_LOCKED) + io_poll_req_insert_locked(req); + else + io_poll_req_insert(req); if (mask && (poll->events & EPOLLET)) { /* can't multishot if failed, just queue the event we've got */ @@ -485,6 +514,15 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags) __poll_t mask = POLLPRI | POLLERR | EPOLLET; int ret; + /* + * apoll requests already grab the mutex to complete in the tw handler, + * so removal from the mutex-backed hash is free, use it by default. + */ + if (issue_flags & IO_URING_F_UNLOCKED) + req->flags &= ~REQ_F_HASH_LOCKED; + else + req->flags |= REQ_F_HASH_LOCKED; + if (!def->pollin && !def->pollout) return IO_APOLL_ABORTED; if (!file_can_poll(req->file)) @@ -534,13 +572,10 @@ int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags) return IO_APOLL_OK; } -/* - * Returns true if we found and killed one or more poll requests - */ -__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk, - bool cancel_all) +static __cold bool io_poll_remove_all_table(struct task_struct *tsk, + struct io_hash_table *table, + bool cancel_all) { - struct io_hash_table *table = &ctx->cancel_table; unsigned nr_buckets = 1U << table->hash_bits; struct hlist_node *tmp; struct io_kiocb *req; @@ -563,6 +598,17 @@ __cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk, return found; } +/* + * Returns true if we found and killed one or more poll requests + */ +__cold bool io_poll_remove_all(struct io_ring_ctx *ctx, struct task_struct *tsk, + bool cancel_all) + __must_hold(&ctx->uring_lock) +{ + return io_poll_remove_all_table(tsk, &ctx->cancel_table, cancel_all) | + io_poll_remove_all_table(tsk, &ctx->cancel_table_locked, cancel_all); +} + static struct io_kiocb *io_poll_find(struct io_ring_ctx *ctx, bool poll_only, struct io_cancel_data *cd, struct io_hash_table *table, @@ -622,13 +668,15 @@ static struct io_kiocb *io_poll_file_find(struct io_ring_ctx *ctx, return NULL; } -static bool io_poll_disarm(struct io_kiocb *req) +static int io_poll_disarm(struct io_kiocb *req) { + if (!req) + return -ENOENT; if (!io_poll_get_ownership(req)) - return false; + return -EALREADY; io_poll_remove_entries(req); hash_del(&req->hash_node); - return true; + return 0; } static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd, @@ -652,7 +700,16 @@ static int __io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd, int io_poll_cancel(struct io_ring_ctx *ctx, struct io_cancel_data *cd, unsigned issue_flags) { - return __io_poll_cancel(ctx, cd, &ctx->cancel_table); + int ret; + + ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table); + if (ret != -ENOENT) + return ret; + + io_ring_submit_lock(ctx, issue_flags); + ret = __io_poll_cancel(ctx, cd, &ctx->cancel_table_locked); + io_ring_submit_unlock(ctx, issue_flags); + return ret; } static __poll_t io_poll_parse_events(const struct io_uring_sqe *sqe, @@ -727,6 +784,16 @@ int io_poll_add(struct io_kiocb *req, unsigned int issue_flags) ipt.pt._qproc = io_poll_queue_proc; + /* + * If sqpoll or single issuer, there is no contention for ->uring_lock + * and we'll end up holding it in tw handlers anyway. + */ + if (!(issue_flags & IO_URING_F_UNLOCKED) && + (req->ctx->flags & (IORING_SETUP_SQPOLL | IORING_SETUP_SINGLE_ISSUER))) + req->flags |= REQ_F_HASH_LOCKED; + else + req->flags &= ~REQ_F_HASH_LOCKED; + ret = __io_arm_poll_handler(req, poll, &ipt, poll->events); if (ret) { io_req_set_res(req, ret, 0); @@ -751,20 +818,28 @@ int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags) bool locked; preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table, &bucket); - if (preq) - ret2 = io_poll_disarm(preq); + ret2 = io_poll_disarm(preq); if (bucket) spin_unlock(&bucket->lock); - - if (!preq) { - ret = -ENOENT; + if (!ret2) + goto found; + if (ret2 != -ENOENT) { + ret = ret2; goto out; } - if (!ret2) { - ret = -EALREADY; + + io_ring_submit_lock(ctx, issue_flags); + preq = io_poll_find(ctx, true, &cd, &ctx->cancel_table_locked, &bucket); + ret2 = io_poll_disarm(preq); + if (bucket) + spin_unlock(&bucket->lock); + io_ring_submit_unlock(ctx, issue_flags); + if (ret2) { + ret = ret2; goto out; } +found: if (poll_update->update_events || poll_update->update_user_data) { /* only mask one event flags, keep behavior flags */ if (poll_update->update_events) { -- 2.7.4