From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759635AbbJ3RW5 (ORCPT ); Fri, 30 Oct 2015 13:22:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750890AbbJ3RW4 (ORCPT ); Fri, 30 Oct 2015 13:22:56 -0400 From: Jeff Moyer To: axboe@kernel.dk, Jason Luo Cc: linux-kernel@vger.kernel.org, Guru Anbalagane , Feng Jin , tj@kernel.org, Ming Lei Subject: [patch, v2] blk-mq: avoid excessive boot delays with large lun counts X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Fri, 30 Oct 2015 13:22:54 -0400 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Zhangqing Luo reported long boot times on a system with thousands of LUNs when scsi-mq was enabled. He narrowed the problem down to blk_mq_add_queue_tag_set, where every queue is frozen in order to set the BLK_MQ_F_TAG_SHARED flag. Each added device will freeze all queues added before it in sequence, which involves waiting for an RCU grace period for each one. We don't need to do this. After the second queue is added, only new queues need to be initialized with the shared tag. We can do that by percolating the flag up to the blk_mq_tag_set, and updating the newly added queue's hctxs if the flag is set. This problem was introduced by commit 0d2602ca30e41 (blk-mq: improve support for shared tags maps). Reported-and-tested-by: Jason Luo Signed-off-by: Jeff Moyer --- Changes from v1: - addressed review comments from Ming, which simplified the patch Jason, if you could sanity test this patch to make sure it still solves your problem, that would be greatly appreciated. diff --git a/block/blk-mq.c b/block/blk-mq.c index 85f0143..12f79af 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1673,7 +1673,7 @@ static int blk_mq_init_hctx(struct request_queue *q, INIT_LIST_HEAD(&hctx->dispatch); hctx->queue = q; hctx->queue_num = hctx_idx; - hctx->flags = set->flags; + hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED; blk_mq_init_cpu_notifier(&hctx->cpu_notifier, blk_mq_hctx_notify, hctx); @@ -1860,27 +1860,26 @@ static void blk_mq_map_swqueue(struct request_queue *q, } } -static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set) +static void queue_set_hctx_shared(struct request_queue *q, bool shared) { struct blk_mq_hw_ctx *hctx; - struct request_queue *q; - bool shared; int i; - if (set->tag_list.next == set->tag_list.prev) - shared = false; - else - shared = true; + queue_for_each_hw_ctx(q, hctx, i) { + if (shared) + hctx->flags |= BLK_MQ_F_TAG_SHARED; + else + hctx->flags &= ~BLK_MQ_F_TAG_SHARED; + } +} + +static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool shared) +{ + struct request_queue *q; list_for_each_entry(q, &set->tag_list, tag_set_list) { blk_mq_freeze_queue(q); - - queue_for_each_hw_ctx(q, hctx, i) { - if (shared) - hctx->flags |= BLK_MQ_F_TAG_SHARED; - else - hctx->flags &= ~BLK_MQ_F_TAG_SHARED; - } + queue_set_hctx_shared(q, shared); blk_mq_unfreeze_queue(q); } } @@ -1891,7 +1890,12 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q) mutex_lock(&set->tag_list_lock); list_del_init(&q->tag_set_list); - blk_mq_update_tag_set_depth(set); + if (set->tag_list.next == set->tag_list.prev) { + /* just transitioned to unshared */ + set->flags &= ~BLK_MQ_F_TAG_SHARED; + /* update existing queue */ + blk_mq_update_tag_set_depth(set, false); + } mutex_unlock(&set->tag_list_lock); } @@ -1901,8 +1905,17 @@ static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set, q->tag_set = set; mutex_lock(&set->tag_list_lock); + + /* Check to see if we're transitioning to shared (from 1 to 2 queues). */ + if (!list_empty(&set->tag_list) && !(set->flags & BLK_MQ_F_TAG_SHARED)) { + set->flags |= BLK_MQ_F_TAG_SHARED; + /* update existing queue */ + blk_mq_update_tag_set_depth(set, true); + } + if (set->flags & BLK_MQ_F_TAG_SHARED) + queue_set_hctx_shared(q, true); list_add_tail(&q->tag_set_list, &set->tag_list); - blk_mq_update_tag_set_depth(set); + mutex_unlock(&set->tag_list_lock); }