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Re: Problems with APIC on versions 4.9 and later (4.8 works)

Em qua., 20 de jan. de 2021 às 12:13, Jürgen Groß <jgross@xxxxxxxx> escreveu:
> On 20.01.21 09:50, Jan Beulich wrote:
> > On 19.01.2021 20:36, Claudemir Todo Bom wrote:
> >> I visually compared all the messages, and the only thing I noticed was that
> >> 4.14 used tsc as clocksource and 4.8 used xen. I tried to boot the kernel
> >> with "clocksource=xen" and the problem is happening with that also.
> >
> > There's some confusion here I suppose: The clock source you talk
> > about is the kernel's, not Xen's. I didn't think this would
> > change for the same kernel version with different Xen underneath,
> > but the Linux maintainers of the Xen code there may know better.
> > Cc-ing them.
> This might depend on CPUID bits given to dom0 by Xen, e.g. regarding
> TSC stability.

Based on this observation I've installed the cpuid utility on the
system and obtained the output of it on all scenarios: raw kernel, xen
4.8.5 and xen 4.14.0.

I used "dom0_max_vcpus=1 dom0_vpus_pin smt=false" on both xen command
lines since this is the only way I can get to a command prompt with
xen 4.14.

the outputs of the cpuid command are attached.

I've compared with diff -u (files also attached):

* the differences of both xen with the raw kernel output
* the differences between both xen

It is clear that xen 4.14 is changing a lot how the dom0 sees the cpu,
disabling a lot of features present both on raw kernel and 4.8
outputs. I don't know if this alone can indicate where the problem is
being triggered.

Next I will try to build xen from source with a "binary tree" approach
between 4.8 and 4.9 commits, but as I will use development source, I
think that is very probable I get with a lot of other problems.

Best regards,

Attachment: cpuid-xen-4.8.txt
Description: Text document

Attachment: cpuid-xen-4.14.txt
Description: Text document

Attachment: cpuid-diff-xen-4.8-4.14.diff
Description: Text Data

Attachment: cpuid-diff-rawkernel-xen-4.8.diff
Description: Text Data

Attachment: cpuid-rawkernel.txt
Description: Text document

Attachment: cpuid-diff-rawkernel-xen-4.14.diff
Description: Text Data



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