Slow boot on rocky linux 10 latest kernel

MajorP93

@TeddyAstie These spinlock events that cause slow boot also happen on my Debian VMs. Also AMD Epyc CPU in my case.

I noticed that this only happens for UEFI enabled VMs. VMs booting in BIOS mode do not have this issue.

TeddyAstie

@MajorP93 can you give the kernel version of all the affected vs non-affected guests ?

olivierlambert

I can reproduce on Debian 13 with stock kernel and a Ryzen 5 7600.

olivierlambert

I'm currently bisecting various kernel builds, I think I'm close to find the culprit.

olivierlambert

Luckily I have enough cores to build a kernel in 2 minutes, because it's been a LOT of them already built to find the culprit

olivierlambert

6.12.90 -> bad
6.12.45 -> bad
6.12.22 -> bad
6.12.11 -> bad
6.12.5 -> bad

BUT 6.12.2 is GOOD! Almost there!

edit: now 6.12.3 is also good. Getting close…

edit: since 6.12.4 is good, then the issue is within 6.12.5. Investigating now.

olivierlambert

Found the culprit, made & tested a patch that works.

Recap at https://notes.vates.tech/share/v5jtq0iytw/p/slow-hvm-boot-on-linux-6-12-5wrvOvZKJ7

I will let the rest of my team to try to get it fixed in upstream.

MajorP93

@olivierlambert Awesome work on tracking down the issue!
Very nice, detailed, technical writeup.

olivierlambert

Ping @Team-Hypervisor-Kernel for reference.

TeddyAstie

@majorp93 @henri9813 @acebmxer
Do you observe the same behavior after setting this for the VM ?

xe vm-param-add uuid=$UUID param-name=platform tsc_mode=2
xe vm-param-add uuid=$UUID param-name=platform nomigrate=true

(beware you lose live migration support doing this, you can cancel these changes with matching vm-param-remove like xe vm-param-remove uuid=$UUID param-name=platform param-key=nomigrate)