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 DBA41D1715A for ; Tue, 22 Oct 2024 11:41:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t3DG1-0005Vf-QF; Tue, 22 Oct 2024 07:41:03 -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 1t3DFp-0005V6-AJ for qemu-devel@nongnu.org; Tue, 22 Oct 2024 07:40:49 -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 1t3DFm-0001MI-4e for qemu-devel@nongnu.org; Tue, 22 Oct 2024 07:40:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1729597242; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=yad+DJ0KMg1UVDaPOPSn50ccXv492VIADa7NYMqPs1I=; b=Jwk3g/1PMVRI+qt9+VkNUgLS/cFXzqi05cMgmUWYoD22DqTavhsG4K1Ss+Wq5ouIfH7NxO hVZFHSWteJWuJuiUM2QPoOtfPSr/R8vuuQzNysl7U+qQ4a7+psa3n6s5yGrP1CfzeG/90G 7+BIkSzgX/BOD1oOxMKZdCwqFo9/nEs= Received: from mx-prod-mc-05.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-48-DHOrHpXbPTiaKRbDHFl3RQ-1; Tue, 22 Oct 2024 07:40:41 -0400 X-MC-Unique: DHOrHpXbPTiaKRbDHFl3RQ-1 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 07595195608D; Tue, 22 Oct 2024 11:40:40 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.150]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4B3B619560AE; Tue, 22 Oct 2024 11:40:39 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 1209D21E6A28; Tue, 22 Oct 2024 13:40:37 +0200 (CEST) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= Cc: Peter Xu , qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Juraj Marcin , Prasad Pandit , Julia Suvorova , Fabiano Rosas Subject: Re: [PATCH] migration: Deprecate query-migrationthreads command In-Reply-To: ("Daniel P. =?utf-8?Q?Berrang?= =?utf-8?Q?=C3=A9=22's?= message of "Tue, 22 Oct 2024 11:43:05 +0100") References: <20241021215220.982325-1-peterx@redhat.com> <87froo34xy.fsf@pond.sub.org> <87jze01kzp.fsf@pond.sub.org> Date: Tue, 22 Oct 2024 13:40:37 +0200 Message-ID: <87plnsz7pm.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.519, 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_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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 Daniel P. Berrang=C3=A9 writes: > On Tue, Oct 22, 2024 at 12:37:46PM +0200, Markus Armbruster wrote: >> Daniel P. Berrang=C3=A9 writes: >>=20 >> > On Tue, Oct 22, 2024 at 10:41:29AM +0200, Markus Armbruster wrote: >> >> Peter Xu writes: >> >>=20 >> >> > Per previous discussion [1,2], this patch deprecates query-migratio= nthreads >> >> > command. >> >> > >> >> > To summarize, the major reason of the deprecation is due to no sens= ible way >> >> > to consume the API properly: >> >> > >> >> > (1) The reported list of threads are incomplete (ignoring destina= tion >> >> > threads and non-multifd threads). >> >> > >> >> > (2) For CPU pinning, there's no way to properly pin the threads w= ith >> >> > the API if the threads will start running right away after mi= gration >> >> > threads can be queried, so the threads will always run on the= default >> >> > cores for a short window. >> >> > >> >> > (3) For VM debugging, one can use "-name $VM,debug-threads=3Don" = instead, >> >> > which will provide proper names for all migration threads. >> >> > >> >> > [1] https://lore.kernel.org/r/20240930195837.825728-1-peterx@redhat= .com >> >> > [2] https://lore.kernel.org/r/20241011153417.516715-1-peterx@redhat= .com >> >> > >> >> > Signed-off-by: Peter Xu >>=20 >> [...] >>=20 >> >> > diff --git a/migration/threadinfo.c b/migration/threadinfo.c >> >> > index 262990dd75..2867413420 100644 >> >> > --- a/migration/threadinfo.c >> >> > +++ b/migration/threadinfo.c >> >> > @@ -13,6 +13,7 @@ >> >> > #include "qemu/osdep.h" >> >> > #include "qemu/queue.h" >> >> > #include "qemu/lockable.h" >> >> > +#include "qemu/error-report.h" >> >> > #include "threadinfo.h" >> >> >=20=20 >> >> > QemuMutex migration_threads_lock; >> >> > @@ -52,6 +53,9 @@ MigrationThreadInfoList *qmp_query_migrationthrea= ds(Error **errp) >> >> > MigrationThread *thread =3D NULL; >> >> >=20=20 >> >> > QEMU_LOCK_GUARD(&migration_threads_lock); >> >> > + >> >> > + warn_report("Command 'query-migrationthreads' is deprecated"); >> >>=20 >> >> We don't normally do this for QMP commands. >> >>=20 >> >> Management applications can use -compat deprecated-input=3Dreject to = check >> >> they're not sending deprecated commands or arguments. >> >>=20 >> >> Suggest to drop. >> > >> > They could, but in practice I don't believe anything is doing this, so >> > the warning message is a practical way to alert people to the usage. >>=20 >> Again, we not normally do this. What makes this one different? > > Do we not ? My expectation is that everything we record in deprecated.rst > also has a corresponding warn_report / warn_report_once in the code. > We know users may not read the docs, so we have a multi-pronged approach > to alerting them. We definitely do not. >> Stepping onto my soapbox: if stuff going away surprisingly would cause >> you enough inconvenience to make early warning desirable, testing with >> suitable -compat is a lot more reliable than relying on warnings. >> *Especially* when your automated testing files warnings unexamined >> together with any other crap that may go to stderr, so your best chance >> to notice the warning is in ad hoc manual testing of QEMU. Nobody does >> that until after things broke. > > I don't see it as an either or choice. We try to surface the deprecation > info in as many different ways as is practical, as no single approach is > going to hit all bases. > > * Document it (deprecated.rst) > * Warn on QEMU stderr if used at runtime (warn_report) > * Enable apps to validate their usage in tests (-compat) > * Mark guests as tainted (libvirt API & VM log file, for certain asepts) To deprecate a QMP command, event, argument or result, we add the feature flag. One-liner, basically impossible to screw up. Review should then catch a missing update to deprecated.rst. Same for un-deprecating something. So far, this is as simple as it could possibly be. That's a feature. A warning requires additional handwritten code. Which *can* be screwed up. Moreover, missing warning (add or delete) is easy to miss in review. If we want such warnings for QMP, they should be automated just like the -compat actions. Any existing warnings rendered redundant should then be taken out. I considered that when I did -compat, and rejected it as not worth the effort.