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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D1B5DC43217 for ; Mon, 28 Nov 2022 13:01:16 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ozdkK-0002TT-HX; Mon, 28 Nov 2022 08:00:28 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ozdkE-0002PQ-DZ for qemu-devel@nongnu.org; Mon, 28 Nov 2022 08:00:23 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ozdkC-0007lb-0M for qemu-devel@nongnu.org; Mon, 28 Nov 2022 08:00:21 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669640419; 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=jrbHP1lBbGFW24fe3r9N1TIkIZ/509WSXjgjV8HPCi0=; b=Q2vCSB4yAVlxV8//DgkwUDhYkEJtwpsjTZh46/xpwxXfSkflRTV2//bKV3IGTPXO5w/W1h yrij1qca/qOa6TN2IaeV0c47Gl5FeH7udtCScykHptjWrajIHoLS4DWkDoLVfKM8WJy99t KlF22lF0ubtZcccXKpbSdNmYAHZlGXY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-247-HcGvEvFxMLS2ymx7FZLaWA-1; Mon, 28 Nov 2022 08:00:15 -0500 X-MC-Unique: HcGvEvFxMLS2ymx7FZLaWA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E2DD13C0F7EC; Mon, 28 Nov 2022 13:00:14 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.100]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2C0842166B4B; Mon, 28 Nov 2022 13:00:13 +0000 (UTC) Date: Mon, 28 Nov 2022 14:00:09 +0100 From: Kevin Wolf To: qemu-block@nongnu.org Cc: eesposit@redhat.com, stefanha@redhat.com, hreitz@redhat.com, pbonzini@redhat.com, vsementsov@yandex-team.ru, qemu-devel@nongnu.org Subject: Re: [PATCH v2 00/15] block: Simplify drain Message-ID: References: <20221118174110.55183-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221118174110.55183-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 18.11.2022 um 18:40 hat Kevin Wolf geschrieben: > I'm aware that exactly nobody has been looking forward to a series with > this title, but it has to be. The way drain works means that we need to > poll in bdrv_replace_child_noperm() and that makes things rather messy > with Emanuele's multiqueue work because you must not poll while you hold > the graph lock. > > The other reason why it has to be is that drain is way too complex and > there are too many different cases. Some simplification like this will > hopefully make it considerably more maintainable. The diffstat probably > tells something, too. > > There are roughly speaking three parts in this series: > > 1. Make BlockDriver.bdrv_drained_begin/end() non-coroutine_fn again, > which allows us to not poll on bdrv_drained_end() any more. > > 2. Remove subtree drains. They are a considerable complication in the > whole drain machinery (in particular, they require polling in the > BdrvChildClass.attach/detach() callbacks that are called during > bdrv_replace_child_noperm()) and none of their users actually has a > good reason to use them. > > 3. Finally get rid of polling in bdrv_replace_child_noperm() by > requiring that the child is already drained by the caller and calling > callbacks only once and not again for every nested drain section. > > If necessary, a prefix of this series can be merged that covers only the > first or the first two parts and it would still make sense. Thanks for the review, applied to block-next. Kevin