From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id 3E3251FF15C for ; Fri, 5 Sep 2025 10:55:19 +0200 (CEST) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 50DF6F86D; Fri, 5 Sep 2025 10:55:33 +0200 (CEST) Message-ID: Date: Fri, 5 Sep 2025 10:54:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Thomas Lamprecht , Proxmox VE development discussion References: <20250904124113.81772-1-f.ebner@proxmox.com> <20250904124113.81772-9-f.ebner@proxmox.com> Content-Language: en-US From: Fiona Ebner In-Reply-To: X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1757062481699 X-SPAM-LEVEL: Spam detection results: 0 AWL -0.023 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Subject: Re: [pve-devel] [PATCH qemu-server v3 stable-bookworm 8/8] migration: preserve host_mtu for virtio-net devices X-BeenThere: pve-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox VE development discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Proxmox VE development discussion Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: pve-devel-bounces@lists.proxmox.com Sender: "pve-devel" Am 04.09.25 um 8:11 PM schrieb Thomas Lamprecht: > Am 04.09.25 um 14:42 schrieb Fiona Ebner: >> The virtual hardware is generated differently (at least for i440fx >> machines) when host_mtu is set or not set on the netdev command line >> [0]. When the MTU is the same value as the default 1500, Proxmox VE >> did not add a host_mtu parameter. This is problematic for migration >> where host_mtu is present on one end of the migration, but not on the >> other [1]. Moreover, the effective setting in the guest (state) will >> still be the host_mtu from the source side, even if a different value >> is used for host_mtu on the target instance's commandline. This will >> not lead to an error loading the migration stream in QEMU, but having >> a larger host_mtu than the bridge MTU is still problematic for certain >> network traffic like >>> iperf3 -c 10.10.10.11 -u -l 2k >> when host_mtu=9000 and bridge MTU=1500. >> >> Pass the values from the source to the target during migration to be >> able to preserve them. > > Which breaks migration from new to old, which can be fine, but seems > avoidable given that we got a tunnel that we can query stuff over. How can we query? The old tunnel only supports very specific commands like 'quit' and 'resume $vmid'. Note that remote migration using the new tunnel version is not broken - an old node will just ignore the additional parameter in the passed-along JSON. We could do something like ssh ... qm start 0 --nets-host-mtu and match for "Unknown option: nets-host-mtu" for detection. Alternatively, we could bump the pve-manager version and guard adding the option via the pmxcfs 'version-info' node kv. That mechanism wasn't super reliable in the past though. > Maybe we could at least catch the "Unknown option: nets-host-mtu" > error explicitly and add some context that the target likely just > needs to be updated to make the migration work. If we don't want to go for either of the above or if there isn't an other way to query, I'll go for that? _______________________________________________ pve-devel mailing list pve-devel@lists.proxmox.com https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel