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 3CB88C54EE9 for ; Tue, 6 Sep 2022 08:09:54 +0000 (UTC) Received: from localhost ([::1]:54374 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oVTeb-0002tm-49 for qemu-devel@archiver.kernel.org; Tue, 06 Sep 2022 04:09:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40070) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oVTY9-0001GY-9S for qemu-devel@nongnu.org; Tue, 06 Sep 2022 04:03:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59929) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oVTY5-0007uH-1n for qemu-devel@nongnu.org; Tue, 06 Sep 2022 04:03:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662451385; 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=pV/edXmhyIj2uUhAVhPjqGaY913SGbpfbYqzYmmsiCw=; b=S7040NhTl9H5m3oXMPbKC9hBOJckFdxkZcReyW3AkgW0Z4mna1dAPTwP+Aecg9Kf4UKikM pB4OGM4X86MRlqJHwpM/aZKroUePVRS6JIyXvEg7SrnwXBKrEpPfJTNRD9V91T/DQiVCW2 pguO+8T0IQwQAMqFLWonCIjX5LRWk5Q= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-438-LRZHJaSdNqKWsPEwVLjwdg-1; Tue, 06 Sep 2022 04:03:02 -0400 X-MC-Unique: LRZHJaSdNqKWsPEwVLjwdg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D9E9A1C01B37; Tue, 6 Sep 2022 08:03:01 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.166]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 85AF32166B26; Tue, 6 Sep 2022 08:03:01 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id E90F421E6900; Tue, 6 Sep 2022 10:02:59 +0200 (CEST) From: Markus Armbruster To: Hyman Huang Cc: Markus Armbruster , qemu-devel , Peter Xu , Juan Quintela , "Dr. David Alan Gilbert" , Eric Blake , Thomas Huth , Laurent Vivier , Paolo Bonzini , "Daniel P. Berrange" Subject: Re: [PATCH v1 3/8] migration: Introduce dirty-limit capability References: <87y1v2w65q.fsf@pond.sub.org> <87y1uykvyu.fsf@pond.sub.org> <4797d938-4638-b12b-c75b-47d291efb6d6@chinatelecom.cn> Date: Tue, 06 Sep 2022 10:02:59 +0200 In-Reply-To: <4797d938-4638-b12b-c75b-47d291efb6d6@chinatelecom.cn> (Hyman Huang's message of "Mon, 5 Sep 2022 21:13:23 +0800") Message-ID: <87pmg93p70.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 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: -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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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" Hyman Huang writes: > =E5=9C=A8 2022/9/5 17:32, Markus Armbruster =E5=86=99=E9=81=93: >> Hyman Huang writes: >>=20 >>> =E5=9C=A8 2022/9/2 16:07, Markus Armbruster =E5=86=99=E9=81=93: >>>> huangy81@chinatelecom.cn writes: >>>> >>>>> From: Hyman Huang(=E9=BB=84=E5=8B=87) >>>>> >>>>> Introduce migration dirty-limit capability, which can >>>>> be turned on before live migration and limit dirty >>>>> page rate durty live migration. >>>>> >>>>> Introduce migrate_dirty_limit function to help check >>>>> if dirty-limit capability enabled during live migration. >>>>> >>>>> Meanwhile, refactor vcpu_dirty_rate_stat_collect >>>>> so that period can be configured instead of hardcoded. >>>>> >>>>> dirty-limit capability is kind of like auto-converge >>>>> but using dirty limit instead of traditional cpu-throttle >>>>> to throttle guest down. To enable this feature, turn on >>>>> the dirty-limit capability before live migration using >>>>> migratioin-set-capabilities, and set the parameters >>>> >>>> migrate-set-capabilities >>>> >>>>> "x-vcpu-dirty-limit-period", "vcpu-dirty-limit" suitably >>>> >>>> "x-vcpu-dirty-limit" >>>> >>>>> to speed up convergence. >>>>> >>>>> Signed-off-by: Hyman Huang(=E9=BB=84=E5=8B=87) >>>> >>>> Hmm. You make dirty-limiting as a whole a stable interface (evidence: >>>> capability "dirty-limit" is stable), but keep its two parameters >>>> unstable. Rationale behind that? >>>> >>> Thanks Markus's comments. :) >>> >>> x-vcpu-dirty-limit-period is an experimental parameter indeed, as to x-= vcpu-dirty-limit, i think it's resonable to be a stable parameter. >>> These 2 parameters are introduced first time and none of them suffer he= avily tests, so i also made vcpu-dirty-limit experimental last version. >>> >>> For dirty-limit interface, it improves the vCPU computational performan= ce during migration indeed(see the test results in cover >>> letter), so it sounds ok to be an stable interface. >>> >>> The 'x-vcpu-dirty-limit-period' parameter can be dropped, IMHO, after b= eing proved insignificant for migration in the future, and meanwhile, >>> x-vcpu-dirty-limit be made stable. >>> >>> Since I don't have much experience to introducing fresh new interface, >>> any suggestions are welcome. >> Is the new interface fit for purpose without use of any experimental >> parameter? >> > If the answer is something like "command dirty-limit improves things >> even without use of experimental parameters, but using them may well >> improve things more (but we need more testing to know for sure)", then >> your current use of 'unstable' may make sense. >>=20 > Yes, with the default value of parameter=EF=BC=8Cthe new interface works = ok and improve performance. > > For x-vcpu-dirty-limit, we provide it because user may not want virtual C= PU throttle heavily, x-vcpu-dirty-limit is kind of like=20 > cpu-throttle-percentage, which is used to setup the threshold when making= guest down. > > For x-vcpu-dirty-limit-period, it is just as you said: "command dirty-lim= it improves things even without use of experimental parameters,=20 > but using them may wellimprove things more (but we need more testing to k= now for sure)" > > So, should i make x-vcpu-dirty-limit non-experimental next version? I think this depends on what exactly you want to signal to users. Your current patch has command dirty-limit stable and the parameters unstable. This signals "go ahead and use dirty-limit, don't worry about the parameters; even if they become stable later, using just dirty-limit will remain okay." If you keep the command unstable as well, you signal the entire interface isn't quite baked, yet. That's a much weaker proposition. So weak in fact that you cannot go wrong :) In short, it boils down to whether you want to encourage use of a part of the evolving interface *now*. Make that part stable. Requires confidence in that part, obviously.