From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2545FC433EF for ; Fri, 15 Apr 2022 09:56:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351932AbiDOJ7A (ORCPT ); Fri, 15 Apr 2022 05:59:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60582 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351938AbiDOJ66 (ORCPT ); Fri, 15 Apr 2022 05:58:58 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06EE3BA306; Fri, 15 Apr 2022 02:56:27 -0700 (PDT) Received: from kwepemi100007.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KfsCR3BnwzfYvB; Fri, 15 Apr 2022 17:55:47 +0800 (CST) Received: from kwepemm600009.china.huawei.com (7.193.23.164) by kwepemi100007.china.huawei.com (7.221.188.115) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 15 Apr 2022 17:56:25 +0800 Received: from huawei.com (10.175.127.227) by kwepemm600009.china.huawei.com (7.193.23.164) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Fri, 15 Apr 2022 17:56:25 +0800 From: Yu Kuai To: , , , , , CC: , , , Subject: [PATCH -next RFC v3 2/8] blk-mq: call 'bt_wait_ptr()' later in blk_mq_get_tag() Date: Fri, 15 Apr 2022 18:10:47 +0800 Message-ID: <20220415101053.554495-3-yukuai3@huawei.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20220415101053.554495-1-yukuai3@huawei.com> References: <20220415101053.554495-1-yukuai3@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.127.227] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm600009.china.huawei.com (7.193.23.164) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org bt_wait_ptr() will increase 'wait_index', however, if blk_mq_get_tag() get a tag successfully after bt_wait_ptr() is called and before sbitmap_prepare_to_wait() is called, then the 'ws' is skipped. This behavior might cause 8 waitqueues to be unbalanced. Move bt_wait_ptr() later should reduce the problem when the disk is under high io preesure. In the meantime, instead of calling bt_wait_ptr() during every loop, calling bt_wait_ptr() only if destination hw queue is changed, which should reduce the unfairness further. Signed-off-by: Yu Kuai --- block/blk-mq-tag.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 68ac23d0b640..5ad85063e91e 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -131,7 +131,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) { struct blk_mq_tags *tags = blk_mq_tags_from_data(data); struct sbitmap_queue *bt; - struct sbq_wait_state *ws; + struct sbq_wait_state *ws = NULL; DEFINE_SBQ_WAIT(wait); unsigned int tag_offset; int tag; @@ -155,7 +155,6 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) if (data->flags & BLK_MQ_REQ_NOWAIT) return BLK_MQ_NO_TAG; - ws = bt_wait_ptr(bt, data->hctx); do { struct sbitmap_queue *bt_prev; @@ -174,6 +173,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) if (tag != BLK_MQ_NO_TAG) break; + if (!ws) + ws = bt_wait_ptr(bt, data->hctx); sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE); tag = __blk_mq_get_tag(data, bt); @@ -199,10 +200,10 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) * previous queue for compensating the wake up miss, so * other allocations on previous queue won't be starved. */ - if (bt != bt_prev) + if (bt != bt_prev) { sbitmap_queue_wake_up(bt_prev); - - ws = bt_wait_ptr(bt, data->hctx); + ws = bt_wait_ptr(bt, data->hctx); + } } while (1); sbitmap_finish_wait(bt, ws, &wait); -- 2.31.1