On 30/1/24 18:09, Ani Sinha wrote:
On 30-Jan-2024, at 22:17, Daniel P. Berrangé <berra...@redhat.com> wrote:
On Tue, Jan 30, 2024 at 10:14:28PM +0530, Ani Sinha wrote:
Since commit f10a570b093e6 ("KVM: x86: Add CONFIG_KVM_MAX_NR_VCPUS to allow up to
4096 vCPUs")
Linux kernel can support upto a maximum number of 4096 vCPUS when MAXSMP is
enabled in the kernel. QEMU has been tested to correctly boot a linux guest
with 1728 vcpus both with edk2 and seabios firmwares. So bump up the max_cpus
value for q35 machines versions 9 and newer to 1728. Q35 machines versions
8.2 and older continue to support 1024 maximum vcpus as before for
compatibility.
Where does the 1728 number come from ?
Did something break at 1729, or did the test machine simply not
have sufficient resources to do practical larger tests ?
Actual limit currently is 1856 for EDK2. The HPE folks tested QEMU with edk2
and QEMU fails to boot beyond that limit.
There are RH internal bugs tracking this and Gerd is working on it from RH side
[1].
We would ultimately like to go to 8192 vcpus for SAP HANA but 1728 vcpus is our
immediate target for now. If you want, I can resend the patch with 1856 since
that is currently the tested limit.
1. https://issues.redhat.com/browse/RHEL-22202
Out of curiosity has the limit to be multiple of 64?
