Reviewed: https://review.opendev.org/695118
Committed:
https://git.openstack.org/cgit/openstack/nova/commit/?id=0e6aac3c2d97c999451da50537df6a0cbddeb4a6
Submitter: Zuul
Branch: master
commit 0e6aac3c2d97c999451da50537df6a0cbddeb4a6
Author: Sean Mooney <w...@seanmooney.info>
Date: Wed Nov 20 00:13:03 2019 +0000
add [libvirt]/max_queues config option
This change adds a max_queues config option to allow
operators to set the maximium number of virtio queue
pairs that can be allocated to a virtio network
interface.
Change-Id: I9abe783a9a9443c799e7c74a57cc30835f679a01
Closes-Bug: #1847367
** Changed in: nova
Status: In Progress => Fix Released
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https://bugs.launchpad.net/bugs/1847367
Title:
Images with hw:vif_multiqueue_enabled can be limited to 8 queues even
if more are supported
Status in OpenStack Compute (nova):
Fix Released
Bug description:
Nova version: 18.2.3
Release: Rocky
Compute node OS: CentOS 7.3
Compute node kernel: 3.10.0-327.13.1.el7.x86_64
In https://bugs.launchpad.net/nova/+bug/1570631 and commit
https://review.opendev.org/#/c/332660/, a bug was fixed by making the
assumption that the kernel version should also dictate the max number
of queues on the tap interface when setting
hw:vif_multiqueue_enabled=True. It was decided that 3.x kernels have a
max queue count of 8. Unfortunately not all distributions follow this,
and CentOS/RHEL has supported up to 256 queues since at least 7.2 even
with a 3.x kernel.
The result of this is that a 20 core VM created in Mitaka will have 20
queues enabled (because the limit of 8 had not been added). The very
same host after being upgraded to Rocky will instead only give 8
queues to the VM even though the kernel supports 256.
Could a workaround option be implemented to disable this check, or
manually define the max queue count?
Snippet of drivers/net/tun.c from CentOS 7.2 kernel source code:
/* MAX_TAP_QUEUES 256 is chosen to allow rx/tx queues to be equal
* to max number of VCPUs in guest. */
#define MAX_TAP_QUEUES 256
#define MAX_TAP_FLOWS 4096
Snippet from the 3.10.0 kernel code from
https://elixir.bootlin.com/linux/v3.10/source/drivers/net/tun.c:
/* DEFAULT_MAX_NUM_RSS_QUEUES were choosed to let the rx/tx queues allocated
for
* the netdevice to be fit in one page. So we can make sure the success of
* memory allocation. TODO: increase the limit. */
#define MAX_TAP_QUEUES DEFAULT_MAX_NUM_RSS_QUEUES
#define MAX_TAP_FLOWS 4096
In the above example, DEFAULT_MAX_NUM_RSS_QUEUES is set to 8.
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