From: Alexander Zeidler <a.zeidler@proxmox.com>
To: pve-devel@lists.proxmox.com
Subject: [pve-devel] [PATCH docs 3/3] qm: resource limits: revise section affinity
Date: Tue, 16 Jan 2024 14:22:40 +0100 [thread overview]
Message-ID: <20240116132240.132246-3-a.zeidler@proxmox.com> (raw)
In-Reply-To: <20240116132240.132246-1-a.zeidler@proxmox.com>
* mention side effects
* increase compactness w/o complexity
* improve section-formatting
Signed-off-by: Alexander Zeidler <a.zeidler@proxmox.com>
---
qm.adoc | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)
diff --git a/qm.adoc b/qm.adoc
index 15aa0fc..d92db75 100644
--- a/qm.adoc
+++ b/qm.adoc
@@ -380,20 +380,24 @@ For more information see `man systemd.resource-control`, here `CPUQuota`
corresponds to `cpulimit` and `CPUWeight` to our `cpuunits` setting. Visit its
Notes section for references and implementation details.
-The third CPU resource limiting setting, *affinity*, controls what host cores
-the virtual machine will be permitted to execute on. E.g., if an affinity value
-of `0-3,8-11` is provided, the virtual machine will be restricted to using the
-host cores `0,1,2,3,8,9,10,` and `11`. Valid *affinity* values are written in
-cpuset `List Format`. List Format is a comma-separated list of CPU numbers and
-ranges of numbers, in ASCII decimal.
-
-NOTE: CPU *affinity* uses the `taskset` command to restrict virtual machines to
-a given set of cores. This restriction will not take effect for some types of
-processes that may be created for IO. *CPU affinity is not a security feature.*
-
-For more information regarding *affinity* see `man cpuset`. Here the
-`List Format` corresponds to valid *affinity* values. Visit its `Formats`
-section for more examples.
+*affinity*
+
+With the *affinity* option you can specify the physical CPU cores which are
+used to run the VM's vCPUs. Periphal VM processes, such as those for I/O, are
+not affected by this setting. Note that the *CPU affinity is not a security
+feature*.
+
+Forcing a CPU *affinity* can make sense in certain cases, but is accompanied by
+an increase in complexity and maintenance effort. For example, if you want to
+add more VMs later or migrate VMs to nodes with fewer CPU cores. It can also
+easily lead to asynchronous and therefore limited system performance if some
+CPUs are fully utilized while others are almost idle.
+
+The *affinity* is set by calling `taskset`. It accepts the host CPU numbers
+(see `lscpu`) in the `List Format` from `man cpuset`. This ASCII decimal list
+can contain numbers but also number ranges. E.g., the *affinity* `0-1,8-11` (or
+alternatively `0,1,8,9,10,11`) only allow the VM to run on these six host
+cores.
CPU Type
^^^^^^^^
--
2.39.2
next prev parent reply other threads:[~2024-01-16 13:23 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-16 13:22 [pve-devel] [PATCH docs 1/3] qm: resource limits: revise section cpulimit Alexander Zeidler
2024-01-16 13:22 ` [pve-devel] [PATCH docs 2/3] qm: resource limits: revise section cpuunits Alexander Zeidler
2024-01-16 13:22 ` Alexander Zeidler [this message]
2024-02-20 12:36 ` [pve-devel] applied-series: [PATCH docs 1/3] qm: resource limits: revise section cpulimit Thomas Lamprecht
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20240116132240.132246-3-a.zeidler@proxmox.com \
--to=a.zeidler@proxmox.com \
--cc=pve-devel@lists.proxmox.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox