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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.11.16 at 17:08, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 28/11/16 15:16, Konrad Rzeszutek Wilk wrote:
>> 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?
> 
> merlot is AMD hardware, so no faulting.
> 
> Also, Xen purposefully leaks EIST into the control domain kernel to work
> around that particular Linux bug.

Isn't EIST an Intel-only thing?

Jan


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