On 01/12/2021 17:17, John Doherty via freebsd-virtualization wrote:
That limitation appears to still exist in FreeBSD 13.0-RELEASE:
[root@grit] # freebsd-version -k ; grep 'VM_MAXCPU'
/usr/src/sys/amd64/include/vmm.h
13.0-RELEASE
#define VM_MAXCPU 16 /* maximum virtual cpus */
I ran into this in May 2021 and with some help from folks on this list
was able to increase it. The simplest (if not minimalist) way to do that
is:
1. edit /usr/src/sys/amd64/include/vmm.h to increase that value: I used 48
2. make buildworld
3. make installworld
The increased value has been working fine for me since I did that. I run
a couple of VMs with 24 vCPUs each and several others with smaller
numbers all the time and have run others with as many as 48 temporarily.
No problems that I have seen.
I am sorry for hijacking this thread but your information is very
interesting. I was playing with VMs in VirtualBox and Bhyve and compared
performance with increasing vCPU count. The more cores VM get the slower
was even a simple single threaded task like loading PF rules from
/etc/pf.conf. It was tested on FreeBSD 11.4 and 12.2, I tested ULE and
4BSD schedulers. Maybe it was somewhat HW related but it always shows
VMs with more than 2 v CPUs significantly slower. VMs with 6+ vCPU was
almost unusable (loading of PF ruleset takes about 8 seconds instead of
fraction on single vCPU VM).
Do you have any special tunning to have so large number of vCPU without
this penalty?
Kind regards
Miroslav Lachman
