RE: [Xen-devel] dom0 is stalled until a keypress

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Joanna Rutkowska [mailto:joanna@xxxxxxxxxxxxxxxxxxxxxx]
> Subject: Re: [Xen-devel] dom0 is stalled until a keypress
> 
> On 09/06/11 17:49, Dan Magenheimer wrote:
> >> From: Rafal Wojtczuk [mailto:rafal@xxxxxxxxxxxxxxxxxxxxxx]
> >> Sent: Monday, September 05, 2011 3:20 AM
> >> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> >> Subject: [Xen-devel] dom0 is stalled until a keypress
> >>
> >> Hello,
> >> The following bizarre behaviour was observed on xen4.1+suse dom0 2.6.38, on
> >> an old Core Duo laptop; maybe someone can hint what is wrong.
> >> Dom0 boot stalls after an init.d script prints "Starting udev". Then 
> >> nothing
> >> seems to happen. I need to press any key to observe progress - I need to do
> >> it tens of times for the boot to finish. After X starts fine, then there is
> >> no need for keypressing anymore.
> >> A particularly disturbing fact is that qrexec_daemon parent, that basically
> >> does
> >> for (;;) { sleep(1); fprintf(stderr, "."); }
> >> does not print dots, until a keypress arrives. So something is very wrong
> >> with timers.
> >> Somehow similarly, pm-suspend sometimes hangs at some stage - after 
> >> detaching
> >> power cord, machine enters S3 immediately.
> >> This is vaguely similar to the issue described in
> >>  https://lkml.org/lkml/2008/9/14/122
> >> but this time, "nohz=off" does not help.
> >>
> >> "cpufreq=dom0-kernel" cures the symptoms; but it is not a sideeffectless
> >> solution. Any idea what is going on or how to debug it ?
> >
> > ISTR seeing this on a Core(2?)Duo laptop and I think the
> > workaround was setting max_cstate=0 (as Xen boot parameter).
> >
> But what was the actual problem? Setting max_cstate is probably even
> worse for power management than setting cpufreq=dom-kernel, isn't it?

Sorry, dunno.  I recall looking into it a bit and finding that
the Core processor (and possibly specifically Merom, the laptop
version) had some special C-state (C3, C1E maybe?) and giving
up at that point.  Sorry I can't be more helpful.

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