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 A4FC2EE57E0 for ; Fri, 8 Sep 2023 09:01:17 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qeXLR-0001dq-1d; Fri, 08 Sep 2023 05:00:06 -0400 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 1qeXLK-0001cV-J9 for qemu-devel@nongnu.org; Fri, 08 Sep 2023 04:59:59 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qeXLH-0005zQ-MR for qemu-devel@nongnu.org; Fri, 08 Sep 2023 04:59:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694163594; 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=RifBq61NLv9aYy4YU7BYrt9MZc6S6d2bw4J3E/bZFT4=; b=TCb5+MP7OAxF24x1rl923N5CoW6Y2yKOgmOTB92dd096+Nrb4uVLOFNnFdqpVoE9GpRF6w yCTy2nZl4cvMlCPhh5sf6+TMZf9VFi34o+IiM7VP3JaM7eYkKo4u7nJCDWPl7w7F6AR57U ZzA7YvnvGvRJd9cRPb3LQ/+zV5NEVXo= 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-82-zZI0UYTsNoWH14s9hE1NeQ-1; Fri, 08 Sep 2023 04:59:51 -0400 X-MC-Unique: zZI0UYTsNoWH14s9hE1NeQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CAD8F1830780; Fri, 8 Sep 2023 08:59:50 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.201]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5F2A9493110; Fri, 8 Sep 2023 08:59:49 +0000 (UTC) Date: Fri, 8 Sep 2023 10:59:48 +0200 From: Kevin Wolf To: Stefan Hajnoczi Cc: qemu-devel@nongnu.org, mst@redhat.com, quintela@redhat.com, peterx@redhat.com, leobras@redhat.com, pbonzini@redhat.com, qemu-block@nongnu.org, qemu-stable@nongnu.org Subject: Re: [PATCH 2/2] virtio: Drop out of coroutine context in virtio_load() Message-ID: References: <20230905145002.46391-1-kwolf@redhat.com> <20230905145002.46391-3-kwolf@redhat.com> <20230907184031.GA1560640@fedora> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="SpUOthRhaeylArR2" Content-Disposition: inline In-Reply-To: <20230907184031.GA1560640@fedora> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@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_H3=0.001, RCVD_IN_MSPIKE_WL=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 --SpUOthRhaeylArR2 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 07.09.2023 um 20:40 hat Stefan Hajnoczi geschrieben: > On Tue, Sep 05, 2023 at 04:50:02PM +0200, Kevin Wolf wrote: > > virtio_load() as a whole should run in coroutine context because it > > reads from the migration stream and we don't want this to block. >=20 > Is that "should" a "must" or a "can"? >=20 > If it's a "must" then virtio_load() needs assert(qemu_in_coroutine()). >=20 > But the previous patch mentioned that loadvm for snapshots calls it > outside coroutine context. So maybe it's a "can"? Where this makes a difference is when the function indirectly calls into QIOChannel. When called from a coroutine, it yields while waiting for I/O, and outside of a coroutine it blocks. Yielding is always preferable, but in cases like HMP savevm/loadvm we also don't really care because it's synchronous anyway. Whether that makes it a MAY or a SHOULD in the RFC sense, you decide. If you wanted to make it a MUST, you'd need to check all callers first and change some of them. 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