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 4EDF8C05027 for ; Fri, 20 Jan 2023 14:01:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pIrxQ-0005YP-1N; Fri, 20 Jan 2023 09:01:28 -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 1pIrxJ-0005QE-MS for qemu-devel@nongnu.org; Fri, 20 Jan 2023 09:01:23 -0500 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pIrxE-0002f9-UL for qemu-devel@nongnu.org; Fri, 20 Jan 2023 09:01:21 -0500 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-368-Fb1KLFPiOdGGSfBsjNHXBw-1; Fri, 20 Jan 2023 09:01:12 -0500 X-MC-Unique: Fb1KLFPiOdGGSfBsjNHXBw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A8606185A78B; Fri, 20 Jan 2023 14:01:11 +0000 (UTC) Received: from kaod.org (unknown [10.39.192.112]) by smtp.corp.redhat.com (Postfix) with SMTP id 125AA40C2064; Fri, 20 Jan 2023 14:00:32 +0000 (UTC) From: Greg Kurz To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi , "Dr. David Alan Gilbert" , Maxime Coquelin , Laurent Vivier , "Michael S. Tsirkin" , Yajun Wu , Peter Maydell , Parav Pandit , qemu-stable@nongnu.org, Greg Kurz Subject: [PATCH 0/2] vhost-user: Remove the nested event loop to unbreak the DPDK use case Date: Thu, 19 Jan 2023 18:24:22 +0100 Message-Id: <20230119172424.478268-1-groug@kaod.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: softfail client-ip=205.139.111.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com X-Spam_score_int: -8 X-Spam_score: -0.9 X-Spam_bar: / X-Spam_report: (-0.9 / 5.0 requ) BAYES_00=-1.9, DATE_IN_PAST_12_24=1.049, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no 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 The nested event loop was introduced in QEMU 6.0 to allow servicing=0D of requests coming from the slave channel while waiting for an ack=0D from the back-end on the master socket. It turns out this is fragile=0D and breaks if the servicing of the slave channel causes a new message=0D to be sent on the master socket. This is exactly what happens when=0D using DPDK as reported in [0].=0D =0D The only identified user for the nested loop is DAX enablement that=0D isn't upstream yet. Just drop the code for now. Some more clever=0D solution should be designed when the need to service concurrent=0D requests from both channels arises again.=0D =0D Greg Kurz (2):=0D Revert "vhost-user: Monitor slave channel in vhost_user_read()"=0D Revert "vhost-user: Introduce nested event loop in vhost_user_read()"=0D =0D hw/virtio/vhost-user.c | 100 ++++-------------------------------------=0D 1 file changed, 8 insertions(+), 92 deletions(-)=0D =0D --=20=0D 2.39.0=0D =0D