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 8B063D16279 for ; Mon, 14 Oct 2024 14:44:50 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t0MJC-00030Z-20; Mon, 14 Oct 2024 10:44:30 -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 1t0MJA-000303-Jv for qemu-devel@nongnu.org; Mon, 14 Oct 2024 10:44:28 -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 1t0MJ8-000439-UN for qemu-devel@nongnu.org; Mon, 14 Oct 2024 10:44:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1728917065; 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=j+bw7SpKEocVmsOAFk05V187KWoXqbzo4/bjxGqP4qs=; b=M+pyvodxlzNbS286elCsv91KGnC9vvgHLKxgl+QOWh5Ukxwbx6OOBME8YMho4MNPF0xaYc HnISHXrTtayQcRH13hjOXymDJGsjHn8TyZReBAl/uBlpajscYnXlA/pE8Od3TVm2B2zVdk 2NloF6ohVaqDg+ZSxDYcfgZ3sxW6Ods= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-592-6KcOJylUOCWFERi1eNAlNA-1; Mon, 14 Oct 2024 10:44:22 -0400 X-MC-Unique: 6KcOJylUOCWFERi1eNAlNA-1 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 146D81955F10; Mon, 14 Oct 2024 14:44:21 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.223]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 336FF19560A2; Mon, 14 Oct 2024 14:44:16 +0000 (UTC) Date: Mon, 14 Oct 2024 15:44:13 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Fabiano Rosas Cc: Peter Xu , qemu-devel@nongnu.org, Juraj Marcin , Markus Armbruster , Prasad Pandit , "Dr . David Alan Gilbert" , Julia Suvorova , Jiang Jiacheng Subject: Re: [PATCH] migration: Remove interface query-migrationthreads Message-ID: References: <20241011153417.516715-1-peterx@redhat.com> <87msj6rcgy.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87msj6rcgy.fsf@suse.de> User-Agent: Mutt/2.2.12 (2023-09-09) 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: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.076, 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, RCVD_IN_SBL_CSS=3.335, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , 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 Mon, Oct 14, 2024 at 11:22:21AM -0300, Fabiano Rosas wrote: > Daniel P. Berrangé writes: > > > On Fri, Oct 11, 2024 at 11:34:17AM -0400, Peter Xu wrote: > >> This reverts two commits: > >> > >> 671326201dac8fe91222ba0045709f04a8ec3af4 > >> 1b1f4ab69c41279a45ccd0d3178e83471e6e4ec1 > >> > >> Meanwhile it adds an entry to removed-features.rst for the > >> query-migrationthreads QMP command. > >> > >> This patch originates from another patchset [1] that wanted to cleanup the > >> interface and add corresponding HMP command, as lots of things are missing > >> in the query report; so far it only reports the main thread and multifd > >> sender threads; all the rest migration threads are not reported, including > >> multifd recv threads. > >> > >> As pointed out by Dan in the follow up discussions [1], the API is designed > >> in an awkward way where CPU pinning may not cover the whole lifecycle of > >> even the thread being reported. When asked, we also didn't get chance to > >> hear from the developer who introduced this feature to explain how this API > >> can be properly used. > >> > >> OTOH, this feature from debugging POV isn't very helpful either, as all > >> these information can be easily obtained by GDB. Esepcially, if with > >> "-name $VM,debug-threads=on" we do already have names for each migration > >> threads (which covers more than multifd sender threads). > >> > >> So it looks like the API isn't helpful in any form as of now, besides it > >> only adds maintenance burden to migration code, even if not much. > >> > >> Considering that so far there's totally no justification on how to use this > >> interface correctly, let's remove this interface instead of cleaning it up. > >> > >> In this special case, we even go beyond normal deprecation procedure, > >> because a deprecation process would only make sense when there are existing > >> users. In this specific case, we expect zero serious users with this API. > > > > We have no way of knowing whether there are existing users of this, or > > any other feature in QEMU. This is why we have a formal deprecation > > period, rather than immediately deleting existing features. > > > > Yes, there are plenty of reasons why this feature is sub-optimal, but > > it is not broken to the extent that it is *impossible* for people to > > be using it. > > > > IOW, I don't see that there's anything special here to justify bypassing > > our deprecation process here. > > I have no dog in this race, but as a data point, I see that this was > submitted to libvirt as a new migrationpin command: > > https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/FVNAUEVIMLG6F2VCRKHZDUEOLBJCXQHO/#BVEGJVZMMLQMXE263GO5BSIWUDIYIFZU And unforunately it seems we dropped the ball on reviewing the v2 of their series and they never ping'd for a response, so this was not merged. Possibly they're just running it as a local patch to libvirt... 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 :|