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 7D952CA0EE6 for ; Tue, 19 Aug 2025 12:08:09 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uoL86-0001Xf-Fx; Tue, 19 Aug 2025 08:07:54 -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 1uoL7z-0001Wl-EN for qemu-devel@nongnu.org; Tue, 19 Aug 2025 08:07:48 -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 1uoL7w-0003yL-6B for qemu-devel@nongnu.org; Tue, 19 Aug 2025 08:07:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1755605261; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Zb+9hjeAiY6NEpGcp1Tjpx6ot7HkyAs8aeY9FuxdUWY=; b=bu4qxc8wCKcdqT5Hi34QFFjXYfszlyIZpBvZgsoroaKXMo5H5a6kdZ1TvZMNTDYL90yM2q gXwHH/aA+2bt96sdj8UkMqz6hkZ0c+Hbi4/5vO3Q5LEAIrORjl+JwwxLoArkQE+bqQkj7I WA2h6bVqZDrzce5Rfk0jg9BMKPB4JqQ= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-466-tDsavxMQOl2nTr-n819IMw-1; Tue, 19 Aug 2025 08:07:36 -0400 X-MC-Unique: tDsavxMQOl2nTr-n819IMw-1 X-Mimecast-MFC-AGG-ID: tDsavxMQOl2nTr-n819IMw_1755605255 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5F1A21800357; Tue, 19 Aug 2025 12:07:35 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.237]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DD35619560AB; Tue, 19 Aug 2025 12:07:32 +0000 (UTC) Date: Tue, 19 Aug 2025 13:07:28 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Lukas Straub Cc: Fabiano Rosas , Peter Xu , Yong Huang , qemu-devel@nongnu.org Subject: Re: [PATCH] multifd: Make the main thread yield periodically to the main loop Message-ID: References: <20250807113639.66d1c5bf@penguin> <20250808090054.13cb8342@penguin> <87o6sp2a0i.fsf@suse.de> <20250811090345.4360fec4@penguin> <878qjq0xtk.fsf@suse.de> <20250819140326.6e94b1c9@penguin> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250819140326.6e94b1c9@penguin> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Aug 19, 2025 at 02:03:26PM +0200, Lukas Straub wrote: > On Tue, 19 Aug 2025 11:31:03 +0100 > Daniel P. Berrangé wrote: > > > On Mon, Aug 11, 2025 at 10:53:11AM -0300, Fabiano Rosas wrote: > > > Lukas Straub writes: > > > > > > > On Fri, 8 Aug 2025 11:37:23 -0400 > > > > Peter Xu wrote: > > > >> ... > > > >> migrate_cancel() should really be an OOB command.. It should be a superset > > > >> of yank features, plus anything migration speficic besides yanking the > > > >> channels, for example, when migration thread is blocked in PRE_SWITCHOVER. > > > > > > > > Hmm, I think the migration code should handle this properly even if the > > > > yank command is used. From the POV of migration, it sees that the > > > > connection broke with connection reset. That is the same error as if the > > > > other side crashes/is killed or a NAT/stateful firewall in between > > > > reboots. > > > > > > > > > > That should all work just fine. After yank or after a detectable network > > > failure. The issue here seems to be that the destination recv is hanging > > > indefinitely. I don't think we ever played with socket timeout > > > configurations, or even switching to non-blocking during the sync. This > > > is actually (AFAIK) the first time we get a hang that's not "just" a > > > synchronization issue in the migration code. > > > > Based on the stack trace, whether the socket is blocking or not isn't a > > problem - QEMU is stuck in a sem_wait call that will delay the coroutine, > > and thus the thread, indefinitely. IMHO the semaphore usage needs to be > > removed in favour of a synchronization mechanism that can integrate with > > event loop such that the coroutine does not block. > > > > I don't think that is an issue. The semaphore is just there to sync > with the multifd threads, which are in turn blocking on recvmsg. > > Without multifd the main thread would hang in recvmsg as well in this > scenario. If it is using blocking I/O that would hang, but that's another thing that should not be done. The QIOChannel code supports using non-blocking sockets in a blocking manner by yielding the coroutine. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|