From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: <a.zeidler@proxmox.com> Received: from firstgate.proxmox.com (firstgate.proxmox.com [212.224.123.68]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.proxmox.com (Postfix) with ESMTPS id CBFE8C1786 for <pve-devel@lists.proxmox.com>; Tue, 16 Jan 2024 14:22:51 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id ACE7F36C08 for <pve-devel@lists.proxmox.com>; Tue, 16 Jan 2024 14:22:51 +0100 (CET) Received: from proxmox-new.maurer-it.com (proxmox-new.maurer-it.com [94.136.29.106]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by firstgate.proxmox.com (Proxmox) with ESMTPS for <pve-devel@lists.proxmox.com>; Tue, 16 Jan 2024 14:22:50 +0100 (CET) Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 9A6BF4914A for <pve-devel@lists.proxmox.com>; Tue, 16 Jan 2024 14:22:50 +0100 (CET) From: Alexander Zeidler <a.zeidler@proxmox.com> To: pve-devel@lists.proxmox.com Date: Tue, 16 Jan 2024 14:22:38 +0100 Message-Id: <20240116132240.132246-1-a.zeidler@proxmox.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SPAM-LEVEL: Spam detection results: 0 AWL 0.053 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 SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record T_SCC_BODY_TEXT_LINE -0.01 - Subject: [pve-devel] [PATCH docs 1/3] qm: resource limits: revise section cpulimit X-BeenThere: pve-devel@lists.proxmox.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Proxmox VE development discussion <pve-devel.lists.proxmox.com> List-Unsubscribe: <https://lists.proxmox.com/cgi-bin/mailman/options/pve-devel>, <mailto:pve-devel-request@lists.proxmox.com?subject=unsubscribe> List-Archive: <http://lists.proxmox.com/pipermail/pve-devel/> List-Post: <mailto:pve-devel@lists.proxmox.com> List-Help: <mailto:pve-devel-request@lists.proxmox.com?subject=help> List-Subscribe: <https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-devel>, <mailto:pve-devel-request@lists.proxmox.com?subject=subscribe> X-List-Received-Date: Tue, 16 Jan 2024 13:22:51 -0000 * precise statements * increase compactness w/o complexity * improve section-formatting Signed-off-by: Alexander Zeidler <a.zeidler@proxmox.com> --- qm.adoc | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-) diff --git a/qm.adoc b/qm.adoc index c2392f3..268a635 100644 --- a/qm.adoc +++ b/qm.adoc @@ -336,31 +336,33 @@ context switches. Resource Limits ^^^^^^^^^^^^^^^ -In addition to the number of virtual cores, you can configure how much resources -a VM can get in relation to the host CPU time and also in relation to other -VMs. -With the *cpulimit* (``Host CPU Time'') option you can limit how much CPU time -the whole VM can use on the host. It is a floating point value representing CPU -time in percent, so `1.0` is equal to `100%`, `2.5` to `250%` and so on. If a -single process would fully use one single core it would have `100%` CPU Time -usage. If a VM with four cores utilizes all its cores fully it would -theoretically use `400%`. In reality the usage may be even a bit higher as QEMU -can have additional threads for VM peripherals besides the vCPU core ones. +*cpulimit* + +In addition to the number of virtual cores, the total available ``Host CPU +Time'' for the VM can be set with the *cpulimit* option. It is a floating point +value representing CPU time in percent, so `1.0` is equal to `100%`, `2.5` to +`250%` and so on. If a single process would fully use one single core it would +have `100%` CPU Time usage. If a VM with four cores utilizes all its cores +fully it would theoretically use `400%`. In reality the usage may be even a bit +higher as QEMU can have additional threads for VM peripherals besides the vCPU +core ones. + This setting can be useful if a VM should have multiple vCPUs, as it runs a few processes in parallel, but the VM as a whole should not be able to run all -vCPUs at 100% at the same time. Using a specific example: lets say we have a VM -which would profit from having 8 vCPUs, but at no time all of those 8 cores -should run at full load - as this would make the server so overloaded that -other VMs and CTs would get to less CPU. So, we set the *cpulimit* limit to -`4.0` (=400%). If all cores do the same heavy work they would all get 50% of a -real host cores CPU time. But, if only 4 would do work they could still get -almost 100% of a real core each. +vCPUs at 100% at the same time. + +Using a specific example: lets say we have a VM which would profit from having +8 vCPUs, but at no time all of those 8 cores should run at full load - as this +would make the server so overloaded that other VMs and CTs would get too less +CPU. So, we set the *cpulimit* limit to `4.0` (=400%). If we now fully utilize +all 8 vCPUs, they will receive maximum 50% CPU time of the physical cores. But +with only 4 vCPUs fully utilized, they could still get up to 100% CPU time. NOTE: VMs can, depending on their configuration, use additional threads, such as for networking or IO operations but also live migration. Thus a VM can show up to use more CPU time than just its virtual CPUs could use. To ensure that a -VM never uses more CPU time than virtual CPUs assigned set the *cpulimit* -setting to the same value as the total core count. +VM never uses more CPU time than vCPUs assigned, set the *cpulimit* to +the same value as the total core count. The second CPU resource limiting setting, *cpuunits* (nowadays often called CPU shares or CPU weight), controls how much CPU time a VM gets compared to other -- 2.39.2