Re: xen 4.11.4 incorrect (~3x) cpu frequency reported

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.07.2021 14:33, James Dingwall wrote:
> Hi Jan,
> 
> Thank you for taking the time to reply.
> 
> On Wed, Jul 21, 2021 at 12:59:11PM +0200, Jan Beulich wrote:
>> On 21.07.2021 11:29, James Dingwall wrote:
>>> We have a system which intermittently starts up and reports an incorrect 
>>> cpu frequency:
>>>
>>> # grep -i mhz /var/log/kern.log 
>>> Jul 14 17:47:47 dom0 kernel: [    0.000475] tsc: Detected 2194.846 MHz 
>>> processor
>>> Jul 14 22:03:37 dom0 kernel: [    0.000476] tsc: Detected 2194.878 MHz 
>>> processor
>>> Jul 14 23:05:13 dom0 kernel: [    0.000478] tsc: Detected 2194.848 MHz 
>>> processor
>>> Jul 14 23:20:47 dom0 kernel: [    0.000474] tsc: Detected 2194.856 MHz 
>>> processor
>>> Jul 14 23:57:39 dom0 kernel: [    0.000476] tsc: Detected 2194.906 MHz 
>>> processor
>>> Jul 15 01:04:09 dom0 kernel: [    0.000476] tsc: Detected 2194.858 MHz 
>>> processor
>>> Jul 15 01:27:15 dom0 kernel: [    0.000482] tsc: Detected 2194.870 MHz 
>>> processor
>>> Jul 15 02:00:13 dom0 kernel: [    0.000481] tsc: Detected 2194.924 MHz 
>>> processor
>>> Jul 15 03:09:23 dom0 kernel: [    0.000475] tsc: Detected 2194.892 MHz 
>>> processor
>>> Jul 15 03:32:50 dom0 kernel: [    0.000482] tsc: Detected 2194.856 MHz 
>>> processor
>>> Jul 15 04:05:27 dom0 kernel: [    0.000480] tsc: Detected 2194.886 MHz 
>>> processor
>>> Jul 15 05:00:38 dom0 kernel: [    0.000473] tsc: Detected 2194.914 MHz 
>>> processor
>>> Jul 15 05:59:33 dom0 kernel: [    0.000480] tsc: Detected 2194.924 MHz 
>>> processor
>>> Jul 15 06:22:31 dom0 kernel: [    0.000474] tsc: Detected 2194.910 MHz 
>>> processor
>>> Jul 15 17:52:57 dom0 kernel: [    0.000474] tsc: Detected 2194.854 MHz 
>>> processor
>>> Jul 15 18:51:36 dom0 kernel: [    0.000474] tsc: Detected 2194.900 MHz 
>>> processor
>>> Jul 15 19:07:26 dom0 kernel: [    0.000478] tsc: Detected 2194.902 MHz 
>>> processor
>>> Jul 15 19:43:56 dom0 kernel: [    0.000154] tsc: Detected 6895.384 MHz 
>>> processor
>>
>> Well, this is output from Dom0. What we'd need to see (in addition)
>> is the corresponding hypervisor log at maximum verbosity (loglvl=all).
> 
> This was just to illustrate that the dom0 usually reports the correct speed.  
> I'll update the xen boot options with loglvl=all and try to collect the boot 
> messages for each case.
> 
>>
>>> The xen 's' debug output:
>>>
>>> (XEN) TSC marked as reliable, warp = 0 (count=4)
>>> (XEN) dom1: mode=0,ofs=0x1d1ac8bf8e,khz=6895385,inc=1
>>> (XEN) dom2: mode=0,ofs=0x28bc24c746,khz=6895385,inc=1
>>> (XEN) dom3: mode=0,ofs=0x345696b138,khz=6895385,inc=1
>>> (XEN) dom4: mode=0,ofs=0x34f2635f31,khz=6895385,inc=1
>>> (XEN) dom5: mode=0,ofs=0x3581618a7d,khz=6895385,inc=1
>>> (XEN) dom6: mode=0,ofs=0x3627ca68b2,khz=6895385,inc=1
>>> (XEN) dom7: mode=0,ofs=0x36dd491860,khz=6895385,inc=1
>>> (XEN) dom8: mode=0,ofs=0x377a57ea1a,khz=6895385,inc=1
>>> (XEN) dom9: mode=0,ofs=0x381eb175ce,khz=6895385,inc=1
>>> (XEN) dom10: mode=0,ofs=0x38cab2e260,khz=6895385,inc=1
>>> (XEN) dom11: mode=0,ofs=0x397fc47387,khz=6895385,inc=1
>>> (XEN) dom12: mode=0,ofs=0x3a552762a0,khz=6895385,inc=1
>>>
>>> A processor from /proc/cpuinfo in dom0:
>>>
>>> processor       : 3
>>> vendor_id       : GenuineIntel
>>> cpu family      : 6
>>> model           : 85
>>> model name      : Intel(R) Xeon(R) D-2123IT CPU @ 2.20GHz
>>> stepping        : 4
>>> microcode       : 0x2000065
>>> cpu MHz         : 6895.384
>>> [...]
>>>
>>> Xen has been built at 310ab79875cb705cc2c7daddff412b5a4899f8c9 from the 
>>> stable-4.12 branch.
>>
>> While this contradicts the title, both 4.11 and 4.12 are out of general
>> support. Hence it would be more helpful if you could obtain respective
>> logs with a more modern version of Xen - ideally from the master branch,
>> or else the most recent stable one (4.15). Provided of course the issue
>> continues to exist there in the first place.
> 
> That was my error, I meant the stable-4.11 branch.  We have a development 
> environment based around 4.14.2 which I can test.

I'm sorry to ask, but have you got around to actually doing that? Or
else is resolving this no longer of interest?

Jan