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Re: [Xen-devel] Regression, host crash with 4.5rc1



On 11/27/2014 01:27 AM, Jan Beulich wrote:
This was precisely the reason why I told you that the numbering
differs (and is confusing and has nothing to do with actual C state
numbers): What max_cstate refers to in the mwait-idle driver is
what above is listed as type[Cx], i.e. the state at index 1 is C1, at
2 we've got C1E, and at 3 we've got C2. And those still aren't in
line with the numbering the CPU documentation uses, it's rather
kind of meant to refer to the ACPI numbering (but probably also
not fully matching up).

Ah, thanks for the explanation.

So max_cstate=2 working suggests a problem with what the CPU
calls C6, which presumably isn't all that surprising considering the
many errata (BD35, BD38, BD40, BD59, BD87, and BD104). Not
sure how to proceed from here - I suppose you already made
sure you run with the latest available BIOS.

Yes, latest available BIOS.

And with 6 errata
documented it's not all that unlikely that there's a 7th one with
MONITOR/MWAIT behavior. The commit you bisected to (and
which you had verified to be the culprit by just forcing
arch_skip_send_event_check() to always return false) could be
reasonably assumed to be broken only when MWAIT use for all
C states didn't work.

Now I did get a hang with max_cstate=3 and mwait-idle=0. May I assume that mwait-idle=0 means that ACPI is responsible for the throttling?

Thanks again for all your help!

Steve

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