Re: [Xen-devel] Latest development (master) Xen fails to boot on HP ProLiant DL20 GEN10

[Roman Shaposhnik <roman@xxxxxxxxxx>]

Btw, forgot to attach the patch with maxcpus=2 -- interestingly enough
Xen seems to hang much further down than before (basically after
attempting to build out Dom0)

On Mon, Sep 30, 2019 at 3:16 PM Roman Shaposhnik <roman@xxxxxxxxxx> wrote:
>
> On Mon, Sep 30, 2019 at 2:56 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >
> > On 28.09.2019 05:07, Roman Shaposhnik wrote:
> > > On Thu, Sep 26, 2019 at 12:44 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > >>
> > >> On 26.09.2019 00:31, Roman Shaposhnik wrote:
> > >>> Jan, Roger, thank you so much for the initial ideas. I tried a few of
> > >>> those and here's where I am.
> > >>>
> > >>> First of all, it is definitely related to CPU bring up. Adding
> > >>> cpuidle=0 to xen command line made Xen boot.
> > >>>
> > >>> Then, a good friend of mine (who you may know from ancient Xen days
> > >>> ;-)) suggested that this could be related to this:
> > >>>      https://wiki.xenproject.org/wiki/Xen_power_management
> > >>> so I went to the BIOS settings and quite to my surprise all of them
> > >>> were grayed out (not tweakable).
> > >>>
> > >>> The only one that wasn't was 2xAPIC support. So just for kicks -- I
> > >>> disabled that.
> > >>>
> > >>> That, in turn, made Xen boot even without cpuidle=0. I'm attaching that 
> > >>> log.
> > >>
> > >> Interesting, but unfortunately this particular log is of no real use
> > >> for investigation of the issue (other than knowing the CPU model). I
> > >> also notice it's a 4.12.0 log, when your original report was against
> > >> latest master.
> > >>
> > >>> So I guess at this point, you could say that I have a functional
> > >>> system, but I'm curious whether you guys would be interested to look
> > >>> into 2xAPIC situation.
> > >>
> > >> Of course we do. As a next step I'd suggest reverting the BIOS settings
> > >> change you did, and instead using the "x2apic=0" Xen command line option.
> > >
> > > Interestingly enough, this doesn't really solve the problem completely.
> > > Specifying x2apic=0 certainly makes Xen go much further to a point
> > > where it tries to load Dom0 and then the console VGA screen goes
> > > blank (this is where that serial debug output would be very useful :-().
> >
> > Now that's again unexpected. In any event you could try "vga=keep".
> >
> > >> And then we of course need a complete boot log (as requested earlier) of
> > >> a problem case.
> > >>
> > >> Further I'd suggest moving away from the black-and-white "cpuidle="
> > >> option, and instead limiting use of deep C states ("max_cstate="). I
> > >> wouldn't be surprised if this was the issue; we'd then have to first
> > >> of all go through errata for the part your system is using.
> > >
> > > Yup. max_cstate=1 makes it boot fine. max_cstate=2 though hangs
> > > the system *exactly* in the same way as specifying x2apic=0
> > > (which is different from the original problem as I've described above).
> >
> > "max_cstate=2" is much less of a "deep" C state than I had expected,
> > but well, so be it then. As to the hang - did you meanwhile figure
> > whether _any_ number of CPUs above 1 would result in a hang, or
> > whether instead there's a certain amount of them that would allow
> > boot to progress fine.
>
> Do you mean by tweaking maxcpus setting?
>
> Anything above 1 doesn't work
>
> maxcpus=1 boots fine tho
>
> > > Can you please elaborate on "we'd then have to first of all go through
> > > errata for the part your system is using"
> >
> > Well, it wouldn't be the first time that hardware had issues with C
> > state handling. Therefore we'd need to (a) be sure you use up-to-date
> > microcode and (b) there are no errata documented for your CPU model
> > workarounds for which basically suggest to avoid use of deep C states.
>
> It seems you've done that already -- thank you!
>
> Thanks,
> Roman.

Attachment: xen3.log
Description: Binary data

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