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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CC885C433EF for ; Wed, 17 Nov 2021 08:07:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FF7E61BD2 for ; Wed, 17 Nov 2021 08:07:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232678AbhKQIKH (ORCPT ); Wed, 17 Nov 2021 03:10:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:39928 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232071AbhKQIKH (ORCPT ); Wed, 17 Nov 2021 03:10:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637136428; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=nilW13qTD/48ImqC9DdVhzc/yeDogF+YeNeQ4Gj89IE=; b=Yx0GeIPs+iKM7DMkCgbN07usx3SBJb/XeZDn4wAgGZV9Z3TqnPE/zc/Hq8TGXFy8KujrkI RkY0foGs0tk3fOaihGsOWD09sWcMgAN+M+6Z8aEprqX3fW/+Hj3SsdQty28RFO8bAUhT28 4uJ4ArOc57QBe4Plzcg3jooYJsNrL58= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-150-P6Z69iaeNAiUp-WUxpRxFA-1; Wed, 17 Nov 2021 03:07:04 -0500 X-MC-Unique: P6Z69iaeNAiUp-WUxpRxFA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 38B101923761; Wed, 17 Nov 2021 08:07:02 +0000 (UTC) Received: from T590 (ovpn-8-24.pek2.redhat.com [10.72.8.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B86F5BAE5; Wed, 17 Nov 2021 08:06:50 +0000 (UTC) Date: Wed, 17 Nov 2021 16:06:45 +0800 From: Ming Lei To: yangerkun Cc: damien.lemoal@wdc.com, axboe@kernel.dk, miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com, linux-block@vger.kernel.org, linux-mtd@lists.infradead.org, yi.zhang@huawei.com, yebin10@huawei.com, houtao1@huawei.com Subject: Re: [QUESTION] blk_mq_freeze_queue in elevator_init_mq Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Nov 17, 2021 at 11:37:13AM +0800, yangerkun wrote: > Nowdays we meet the boot regression while enable lots of mtdblock What is your boot regression? Any dmesg log? > compare with 4.4. The main reason was that the blk_mq_freeze_queue in > elevator_init_mq will wait a RCU gap which want to make sure no IO will > happen while blk_mq_init_sched. There isn't RCU grace period implied in the blk_mq_freeze_queue() called from elevator_init_mq(), because the .q_usage_counter works at atomic mode at that time. > > Other module like loop meets this problem too and has been fix with Again, what is the problem? > follow patches: > > 2112f5c1330a loop: Select I/O scheduler 'none' from inside add_disk() > 90b7198001f2 blk-mq: Introduce the BLK_MQ_F_NO_SCHED_BY_DEFAULT flag > > They change the default IO scheduler for loop to 'none'. So no need to > call blk_mq_freeze_queue and blk_mq_init_sched. But it seems not > appropriate for mtdblocks. Mtdblocks can use 'mq-deadline' to help > optimize the random write with the help of mtdblock's cache. Once change > to 'none', we may meet the regression for random write. > > commit 737eb78e82d52d35df166d29af32bf61992de71d > Author: Damien Le Moal > Date: Thu Sep 5 18:51:33 2019 +0900 > > block: Delay default elevator initialization > > ... > > Additionally, to make sure that the elevator initialization is never > done while requests are in-flight (there should be none when the device > driver calls device_add_disk()), freeze and quiesce the device request > queue before calling blk_mq_init_sched() in elevator_init_mq(). > ... > > This commit add blk_mq_freeze_queue in elevator_init_mq which try to > make sure no in-flight request while we go through blk_mq_init_sched. > But does there any drivers can leave IO alive while we go through > elevator_init_mq？ And if no, maybe we can just remove this logical to > fix the regression... SCSI should have passthrough requests at that moment. Thanks, Ming