Re: PHP performance on Xen domU with mulitple vcpu

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Sun, Apr 06, 2025 at 11:50:37PM +0000, Emmanuel Dreyfus wrote:
> I restarted with stock 10.0 XEN3_DOMU kernel to get dtrace working
> (it does not), but now the problem seems to have vanished.

I have a domU carrying a busy web server. I upgraded vcpus from
1 to 4, and the time keeping bug pops up within a few hours.
ntpd gets unable to keep in sync, and clock quickly drift.

After 40 minutes of utpime, I already have toublesome outout from
the test counting how many time gettimefday() returns the same value.
Here is an example for 1000 calls:
227 1747527666.919678
204 1747527666.919679
2 1747527666.925902
38 1747527666.925914
4 1747527666.926081
2 1747527666.926099
2 1747527666.926107
4 1747527666.926120
1 1747527666.926135
2 1747527666.926141
2 1747527666.926151
6 1747527666.926159
1 1747527666.926189
1 1747527666.926194
79 1747527666.926201
425 1747527666.926202

That suggests the bug is easier to reproduce with more vcpus.

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost