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 CE28FC433FE for ; Thu, 10 Nov 2022 20:13:41 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1otDvU-0005UO-SC; Thu, 10 Nov 2022 15:13:28 -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 1otDvT-0005T5-8z for qemu-devel@nongnu.org; Thu, 10 Nov 2022 15:13:27 -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 1otDvR-0006ev-33 for qemu-devel@nongnu.org; Thu, 10 Nov 2022 15:13:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668111203; 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=lqr7VUbpPq8ogAfTtgpo9D+706sGDP3PKwkmcQ7YylQ=; b=TuADeMxlRV0ANSOidWiZC6jw6lkGG40JuZZe9RiLKHTNVj1pE/WBWJDnNWjjaewBZvgDbL T7bHUCx7DnYHRBEPJGg/hOj6l/v/5M3cTwuJ2XRoBXxD5OUhCO8c7sHM4541D1QZ55n9ut AbDyzLDyob3aiIBNmfgQDKsm9zZJh5Q= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-39-AlO2iFIpOTmQa2Y-TMN-HQ-1; Thu, 10 Nov 2022 15:13:21 -0500 X-MC-Unique: AlO2iFIpOTmQa2Y-TMN-HQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 49A59800B23; Thu, 10 Nov 2022 20:13:21 +0000 (UTC) Received: from localhost (unknown [10.39.192.6]) by smtp.corp.redhat.com (Postfix) with ESMTP id BABCD1121330; Thu, 10 Nov 2022 20:13:20 +0000 (UTC) Date: Thu, 10 Nov 2022 15:13:18 -0500 From: Stefan Hajnoczi To: Kevin Wolf Cc: qemu-block@nongnu.org, eesposit@redhat.com, hreitz@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 00/13] block: Simplify drain Message-ID: References: <20221108123738.530873-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="+yTjzFkndmeZbkxy" Content-Disposition: inline In-Reply-To: <20221108123738.530873-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 --+yTjzFkndmeZbkxy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Nov 08, 2022 at 01:37:25PM +0100, Kevin Wolf wrote: > 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. >=20 > 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. >=20 > There are roughly speaking three parts in this series: >=20 > 1. Make BlockDriver.bdrv_drained_begin/end() non-coroutine_fn again, > which allows us to not poll on bdrv_drained_end() any more. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > Kevin Wolf (13): > qed: Don't yield in bdrv_qed_co_drain_begin() > test-bdrv-drain: Don't yield in .bdrv_co_drained_begin/end() > block: Revert .bdrv_drained_begin/end to non-coroutine_fn > block: Remove drained_end_counter > block: Inline bdrv_drain_invoke() > block: Drain invidual nodes during reopen > block: Don't use subtree drains in bdrv_drop_intermediate() > stream: Replace subtree drain with a single node drain > block: Remove subtree drains > block: Call drain callbacks only once > block: Remove ignore_bds_parents parameter from drain functions > block: Don't poll in bdrv_replace_child_noperm() > block: Remove poll parameter from bdrv_parent_drained_begin_single() >=20 > include/block/block-global-state.h | 3 + > include/block/block-io.h | 52 +--- > include/block/block_int-common.h | 17 +- > include/block/block_int-io.h | 12 - > block.c | 132 ++++++----- > block/block-backend.c | 4 +- > block/io.c | 281 ++++------------------ > block/qed.c | 24 +- > block/replication.c | 6 - > block/stream.c | 20 +- > block/throttle.c | 6 +- > blockdev.c | 13 - > blockjob.c | 2 +- > tests/unit/test-bdrv-drain.c | 369 +++++++---------------------- > 14 files changed, 270 insertions(+), 671 deletions(-) I have looked through all patches but don't understand the code well enough to give an opinion or spot bugs. Removing subtree drains and aio_poll() in bdrv_replace_child_noperm() are nice. Acked-by: Stefan Hajnoczi --+yTjzFkndmeZbkxy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmNtW14ACgkQnKSrs4Gr c8jfqAgApu7tq7JqW6c50BA89aV3Bxad4YXDzBe5vh4VRvrAZJZes7pfce4hxnpt QXZrJh+4yS7xD0XuD5DLVh4SQMZf0NRkgAj98KOzP9HMOw0OinepcokGpJhn+5wl ARo5IKP5d63lQC4h+We+bg0OYsNfaj3GftvwKYAND/E+vtZjBiS0QCogzqVNRxl5 uPkrHHXm3pn8Ue120Fx+bm3WVvMQJRCQTArot/Nj1e+UuHv348kcmjA8rN7kiUVn q9ciFL/+BRTDhwCgqHDVFwiOAmRPjXgydsPEYBVbkE24keaCJGPYQbByS0b3KUSr YzeYjwzd/bbR/Os6t2LjrUzNTZUWlw== =mp2k -----END PGP SIGNATURE----- --+yTjzFkndmeZbkxy--