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 6B62DC43334 for ; Thu, 30 Jun 2022 10:16:11 +0000 (UTC) Received: from localhost ([::1]:36702 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o6rDW-0003WW-At for qemu-devel@archiver.kernel.org; Thu, 30 Jun 2022 06:16:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42894) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o6rC7-0002ft-JV for qemu-devel@nongnu.org; Thu, 30 Jun 2022 06:14:43 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:36118) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1o6rC5-0005pB-LQ for qemu-devel@nongnu.org; Thu, 30 Jun 2022 06:14:43 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id BD28B1F8D0; Thu, 30 Jun 2022 10:14:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1656584077; h=from:from:reply-to: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=6ShA4hzmsgK6sDdz75gmlsG55c005tHJw2XA+sysORA=; b=HGpX3YYZu6jk+Wznq6S56r7bHm2ZYSWySCcQNFvyamyjj4ynyxnrros6Xw8m+bNx7RuvCZ y/IaTHqJ432fNJkSS6lFmwN16O8w+zUEOW6liqcbQ/j/V5EJ+592p2W5LzW3D6JOE1/byC UWBBmpgy/CRdAKMUSv/hjE6IbHTUjPU= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1656584077; h=from:from:reply-to: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=6ShA4hzmsgK6sDdz75gmlsG55c005tHJw2XA+sysORA=; b=n3zFXrRJkmHL1j4aCYi68KkqsSjrGOoSGjOtNlbQ5/m+6tPx8vEnbMMlO+1Gz7p+EEXtW2 KdMoIgLW7EXBWGCA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 04DC413A5C; Thu, 30 Jun 2022 10:14:36 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id vXpPOox3vWJwdgAAMHmgww (envelope-from ); Thu, 30 Jun 2022 10:14:36 +0000 Message-ID: <2341fe7b-9831-24eb-c78c-39497901eea9@suse.de> Date: Thu, 30 Jun 2022 12:14:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PULL 15/18] qapi: introduce x-query-ramblock QMP command Content-Language: en-US To: "Dr. David Alan Gilbert" , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= Cc: qemu-devel@nongnu.org, Laurent Vivier , Thomas Huth , Eduardo Habkost , David Hildenbrand , Michael Roth , Richard Henderson , Yuval Shaia , Peter Xu , Gerd Hoffmann , Paolo Bonzini , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Eric Blake , Markus Armbruster References: <20211102175700.1175996-1-berrange@redhat.com> <20211102175700.1175996-16-berrange@redhat.com> <073c1687-d30f-8f41-b87e-83372137708a@suse.de> From: Claudio Fontana In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=195.135.220.29; envelope-from=cfontana@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_MED=-2.3, 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" On 6/9/22 14:52, Dr. David Alan Gilbert wrote: > * Daniel P. Berrangé (berrange@redhat.com) wrote: >> On Thu, Jun 09, 2022 at 12:07:31PM +0200, Claudio Fontana wrote: >>> Hello all, >>> >>> it would be really good to be able to rely on this command or something similar, >>> to be able to know the approximate size of a migration before starting it. >>> >>> in QEMU ram_bytes_total() returns what I would like to have, >>> but there is currently no QMP way to get it without starting a migration, >>> which when trying to optimize it/size it is just about too late. >> >> Aside from the main VM RAM, what other RAM blocks are likely to have >> a size large enough to be of consequence to the live migration >> data copy, and whose size is not already known to the mgmt app from >> the guest config choices it made ? VGA RAM could be a few 100MB I >> guess, but the mgmt app knows about that. I've always assumed everything >> else is just noise in comparison to the main RAM region. >> >> Still I wonder how useful this is as its just a static figure, and the >> problems with migration transfer are the bulking up of data when the >> VM is repeatedly dirtying stuff at a high rate. >> >>> Do you think x-query-ramblock could be promoted to non-experimental? >> >> It would have to be re-written, as this current impl is just emitting >> a huge printf formatted string. To be considered supportable, the data >> would have to be formally modelled in QAPI instead. >> >> IOW, it would be a case of introducing a new command that emits formal >> data, convertintg 'info ramblock' to use that, and then deprecating this >> x-query-ramblock. >> >>> Should another one be made available instead, like : >>> query-ram-bytes-total ? >> >> That would be simpler if you're just wanting it to give a single >> figure. > > Is this what qmp_query_memory_size_summary does? No, I am not looking at something returning the machine->ram_size, but rather how many bytes are actually used in each RAMBlock, in order to estimate the transfer size of a guest to disk. This would be the return value of something like migration/ram.c::ram_bytes_total(). The main guest RAM total size is in most cases an overestimation of the actual bytes required to be transferred. If there was such a feature that just returns ram_bytes_total via QMP, by knowing the size in bytes before the transfer, we can prealloc the space on disk, which would improve the performance of this series: https://patchew.org/Libvirt/20220607091936.7948-1-cfontana@suse.de/ The interleaved format I posted there works just fine to migrate a suspended VM to disk (virsh save) from multifd channels to a single file, but still incurs in a 4-5% performance penalty compared with the multiple files approach, that is apparently due to multiple threads competing on acquiring locks to adjust the file size (on XFS). Doing a fallocate() would likely remove this performance decrease compared with multifd to multiple files, but requires knowing beforehand the approximate size of the transfer, and as mentioned mnachine->ram_size is just overkill in practice and risks erroring out if not enough space is available. Feedback on the interleaved format I posted there is welcome as well, Thanks, Claudio > > Dave > >> >> 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 :| >>