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

[James Dingwall <james-xen@xxxxxxxxxxxxxx>]

Hi Jan,

On Fri, Nov 05, 2021 at 01:50:04PM +0100, Jan Beulich wrote:
> 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?

We have recorded a couple of other occurences on 4.11 but it is happening so
infrequently (probably once every few hundred boots) that further investigation
is low on a long list of tasks.  We are also moving to 4.14.3 and so far have
no occurences with that version.

Thanks,
James