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

[Rafal Wojtczuk <rafal@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Sep 07, 2011 at 10:35:45AM +0100, Jan Beulich wrote:
> >>> On 07.09.11 at 11:03, Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx> 
> >>> wrote:
> > On 09/06/11 19:17, Dan Magenheimer wrote:
> >>> 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.
> > 
> > But the same system worked fine without any tweaks (cpufreq, max_cstate)
> > on Xen 3.4 and only started exhibiting this behavior after we switched
> > to Xen 4.1...
> 
> 4.1.0 or 4.1.1?
Originally tested on 4.1.0; same problem with 4.1.1.

Jeremy> Try booting with "idle=halt".
It does not help, either.

Regards,
RW

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