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 3E5C4C433EF for ; Wed, 10 Nov 2021 10:46:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C25161168 for ; Wed, 10 Nov 2021 10:46:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231214AbhKJKsy (ORCPT ); Wed, 10 Nov 2021 05:48:54 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:28943 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229653AbhKJKsx (ORCPT ); Wed, 10 Nov 2021 05:48:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636541165; 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: in-reply-to:in-reply-to:references:references; bh=eqCttD3Xd5hwRL+t63xG9x7gvxrIP+8WdXxav6/uzGQ=; b=dNV+lAx9O58dlRi9AD1xRLmeVlv8dTnK8pwDwNqGaQtJsa92PGnHjN319firljtGddy4Bz OUdy6hqXC2xJvf4c9ozUsXZpJTH/C3HV20EFkMyIMguGFr3XStY+yZ1q4kIBQrPP5aHL0M Pi/gjLbTl8JZi40ID1gynhGc3VEhP/M= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-247-7ug1M-ffNG6h2smBDU4Y7Q-1; Wed, 10 Nov 2021 05:46:02 -0500 X-MC-Unique: 7ug1M-ffNG6h2smBDU4Y7Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DD6CE871803; Wed, 10 Nov 2021 10:46:00 +0000 (UTC) Received: from T590 (ovpn-8-19.pek2.redhat.com [10.72.8.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 34E4410074E0; Wed, 10 Nov 2021 10:45:56 +0000 (UTC) Date: Wed, 10 Nov 2021 18:45:52 +0800 From: Ming Lei To: Hannes Reinecke Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-nvme@lists.infradead.org Subject: Re: sorting out the freeze / quiesce mess Message-ID: References: <20211110091407.GA8396@lst.de> <477f3098-39be-ad07-e2fb-3ef3309c4dce@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <477f3098-39be-ad07-e2fb-3ef3309c4dce@suse.de> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Nov 10, 2021 at 11:22:05AM +0100, Hannes Reinecke wrote: > On 11/10/21 10:14 AM, Christoph Hellwig wrote: > > Hi Jens and Ming, > > > > I've been looking into properly supporting queue freezing for bio based > > drivers (that is only release q_usage_counter on bio completion for them). > > And the deeper I look into the code the more I'm confused by us having > > the blk_mq_quiesce* interface in addition to blk_freeze_queue. What > > is a good reason to do a quiesce separately from a freeze? > > > IIRC the 'quiesce' interface was an abstraction from the SCSI 'quiesce' > operation, where we had to stop all I/O except for TMFs and scanning. > And 'freeze' was designed fro stopping all I/O. > > But I'm not sure if that ever was the distinction, or if it still > applies today. > > And yeah, I've been wondering myself. > > Probably we should just kill the 'quiesce' stuff and see where we end up :-) In case of EH, no queued requests can be completed, however driver still needs to stop queue and reset hardware, then how can you use freeze to stop queue? See nvme_dev_disable(). Freeze can stop to allocate new request and drain all queued requests, but it can't prevent IO from being queued to LLD. On the contrary, blk_mq_freeze_queue_wait() requires LLD to handle IO for moving on, otherwise it will wait forever. Thanks, Ming