Re: [Xen-devel] some thoughts about merlot{0|1} issues [was: Re: [xen-unstable test] 102522: tolerable FAIL - PUSHED]

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Nov 28, 2016 at 08:48:30AM -0500, Boris Ostrovsky wrote:
> On 11/24/2016 10:31 AM, Jan Beulich wrote:
> >>>> On 24.11.16 at 16:14, <dario.faggioli@xxxxxxxxxx> wrote:
> >> When dumping ACPI C states, here's how things look like for _all_ CPUs:
> >> Nov 23 13:13:00.382134 (XEN) ==cpu3==
> >> Nov 23 13:13:00.382157 (XEN) active state:         C-1
> >> Nov 23 13:13:00.390096 (XEN) max_cstate:           C7
> >> Nov 23 13:13:00.390125 (XEN) states:
> >> Nov 23 13:13:00.390148 (XEN)     C1:       type[C1] latency[000] 
> >> usage[00000000] method[ HALT] duration[0]
> >> Nov 23 13:13:00.398055 (XEN)     C0:       usage[00000000] 
> >> duration[4229118701384]
> >> Nov 23 13:13:00.398090 (XEN) PC2[0] PC3[0] PC6[0] PC7[0]
> >> Nov 23 13:13:00.406088 (XEN) CC3[0] CC6[0] CC7[0]
> >>
> >> And I checked other runs, and it's the same everywhere.
> >>
> >> I remember that Jan suggested trying to pass max_cstate=1 to Xen at
> >> boot. I was about to ask Ian to do that for this host, but it looks
> >> like we're using only C0 and C1 already anyway.
> > This indeed looks surprising for a half way modern system - is the
> > BIOS perhaps limiting C-states (maybe instructed to via BIOS setup)?
> 
> 
> IIRC some BIOSes indeed provided an option to disable C2. Dumping SSDT
> would tell us whether C2 is there is BIOS is not accessible.

Keep in mind that not all C states are exposed if MWAIT is not exposed
to dom0 (see xen_check_mwait in arch/x86/xen/enlighten.c).

I recall some emails from Andrew about the CPU faulting and his CPUID
patches inhibiting this but it may very well be fixed?

Dario, lastly - did you have xen-acpi-processor loaded or built in your kernel?
> 
> -boris
> 
> 
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