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 ws5-mx01.kavi.com (ws5-mx01.kavi.com [34.193.7.191]) (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 D04F1C197A0 for ; Fri, 17 Nov 2023 13:58:36 +0000 (UTC) Received: from lists.oasis-open.org (oasis.ws5.connectedcommunity.org [10.110.1.242]) by ws5-mx01.kavi.com (Postfix) with ESMTP id 2D95541F28 for ; Fri, 17 Nov 2023 13:58:36 +0000 (UTC) Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 0D54A986E2D for ; Fri, 17 Nov 2023 13:58:36 +0000 (UTC) Received: from host09.ws5.connectedcommunity.org (host09.ws5.connectedcommunity.org [10.110.1.97]) by lists.oasis-open.org (Postfix) with QMQP id E9635986E21; Fri, 17 Nov 2023 13:58:35 +0000 (UTC) Mailing-List: contact virtio-comment-help@lists.oasis-open.org; run by ezmlm List-ID: Sender: Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id D965A986E24 for ; Fri, 17 Nov 2023 13:58:35 +0000 (UTC) X-Virus-Scanned: amavisd-new at kavi.com X-MC-Unique: crS659MyMFCD8yO3p_pBmw-1 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1700229512; x=1700834312; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=ACM1TKIgPA9pTXMR2IifAs9QbgzJs67mlDwFcVDGRmk=; b=q0mZHf35+cxYfOhomSUgAI6+5ZqtEWOuRnmDmj5jInfPzOs7Zh02gGFXsWinIH4jot fpiD4M3iY2O9zEusJTn7gOCMd1dwbhtgwptpfLjCUQ+uqRje+FL6/jhf18eUL6Frme3Z 57ygBf/MS9JtKu3KtiRT8YkI5gecKh63K2cGeRki+lRAHb1ibwBzIfoPmaAZL/x4Ysvo F0qPUxLepcwWgxu0MU5iM46xamnHk/h+G+bw76U8756QTQjUA846lZz6JbR9leh0Pgvu cauyWpbQMfEX0He0SlXAul5KSZZubHr4bnV3yu/wL6X/oOHoYxDNbS0CtfppFFzC2K9D 8oJg== X-Gm-Message-State: AOJu0YzKJbfcxphOF8gUjUUz0vaharA5QHIKAZaeGygKBSnA8KravBoI o3hmM7sU34UVQ8Fxfh76MH2uaUzQc9SEl4Uyk5P4+jdlzBS+kgZVOWTMBgdyMtEtP7r1v7mt4G2 1cg86ZgIHnd5yQZ8GQQB3QKQ9sDQYpEfq6w== X-Received: by 2002:adf:f392:0:b0:32d:570b:c0a4 with SMTP id m18-20020adff392000000b0032d570bc0a4mr12135983wro.27.1700229512666; Fri, 17 Nov 2023 05:58:32 -0800 (PST) X-Google-Smtp-Source: AGHT+IFZUSLerJt7Jo8iDNGD0pL0uKhKOOkG0i/5Kx97Wxe5PNvpMpvW8NeIiWZ87Xz8KaOtwF2Wcg== X-Received: by 2002:adf:f392:0:b0:32d:570b:c0a4 with SMTP id m18-20020adff392000000b0032d570bc0a4mr12135963wro.27.1700229512352; Fri, 17 Nov 2023 05:58:32 -0800 (PST) Date: Fri, 17 Nov 2023 08:58:25 -0500 From: "Michael S. Tsirkin" To: Parav Pandit Cc: Jason Wang , "virtio-comment@lists.oasis-open.org" , "cohuck@redhat.com" , "sburla@marvell.com" , Shahaf Shuler , Maor Gottlieb , Yishai Hadas , "lingshan.zhu@intel.com" Message-ID: <20231117085422-mutt-send-email-mst@kernel.org> References: <20231117050838-mutt-send-email-mst@kernel.org> <20231117061122-mutt-send-email-mst@kernel.org> <20231117064344-mutt-send-email-mst@kernel.org> <20231117073250-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Subject: Re: [virtio-comment] Re: [PATCH v3 6/8] admin: Add theory of operation for write recording commands On Fri, Nov 17, 2023 at 12:49:36PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin > > Sent: Friday, November 17, 2023 6:07 PM > > To: Parav Pandit > > > > On Fri, Nov 17, 2023 at 12:15:54PM +0000, Parav Pandit wrote: > > > Hi Alex, Jason, > > > > > > > From: Michael S. Tsirkin > > > > Sent: Friday, November 17, 2023 5:20 PM > > > > To: Parav Pandit > > > > > > > > > Allocating resources on outgoing migration is a very bad idea. > > > > > > It is common to migrate prcisely because you are out of resources. > > > > > > Incoming is a different story, less of a problem. > > > > > > > > > > > The resource allocated may not be on same system. > > > > > Also the resource allocated while the VM is running, so I don’t see a > > problem. > > > > > > > > > Additionally, this is not what the Linux kernel maintainers of > > > > > iommu subsystem > > > > told us either. > > > > > Let me know if you check with Alex W and Jason who build this interface. > > > > > > > > VFIO guys have their own ideas, if they want to talk to virtio guys > > > > they can come here and do that. > > > > > > Since one of the use cases would have accepted to let dirty tracking to fail, I > > dont see a problem. > > > This is not the only command on source that fails. > > > So I anticipate that QEMU and libvirt or any vfio user would build the > > orchestration around the possible failure because the UAPI is well defined. > > > > > > When there is hypervisor, that must have zero failures on src side, such kernel > > + device can build everything reserved upfront. > > > > > > Do you say, QEMU has zero memory allocations on source side for migration? > > > That would be interesting to know. > > > > More or less yes. More precisely while in theory allocations it's doing can fail in > > practice it happens rarely enough that QEMU does not even bother checking > > and will immediately crash if they do. The reason is that it's using virtual > > memory, so it scales to a huge number of VMs. > > Migrating a single VM at a time is not even worth discussing. > > Wow that is even much worse to crash the running VM, instead of failing the migration. I am telling you. It does not practically crash because it does not allocate physical memory. > I have live migrated VMs one by one and have seen customers migrate on hyperconverged systems. Ofcourse it was not QEMU. > Single VM migration is real and used by cloud operators. > Why would you ignore it? I guess they only have single tenant hosts then? Because each tenant might request migration at any time. -- MST This publicly archived list offers a means to provide input to the OASIS Virtual I/O Device (VIRTIO) TC. 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