Re: [REGRESSION from 2.6.23-rc8] (was: Re: 2.6.23-rc4-mm1 and -rc6-mm1: boot failure on HP nx6325, related to clockevents)

[Rafael J. Wysocki]

Thomas,

On Wednesday, 26 September 2007 23:34, Thomas Gleixner wrote:
> Rafael,
> 
> On Wed, 2007-09-26 at 23:00 +0200, Rafael J. Wysocki wrote:
> > > > > First, with the "x86-64: Disable local APIC timer use on AMD systems with C1E"
> > > > > patch and my collection of suspend patches applied, the box doesn't boot
> > > > > (the suspend patches don't even thouch the boot code, so they should be
> > > > > irrelevant here).  However, it boots if patch-2.6.23-rc7-hrt1.patch (adjusted
> > > > > for 2.6.23-rc8) is applied in addition.  Is this expected?
> > > > 
> > > > No. That's odd. It is nothing else than adding "noapictimer" to the
> > > > kernel command line.
> > > 
> > > Seems to be reproducible, though.  I'll investigate further.
> > 
> > So far, the results are the following:
> > 
> > 1) current Linus' tree doesn't boot with any command line (regression)
> > 
> > [  Linus, please revert commit e66485d747505e9d960b864fc6c37f8b2afafaf0
> > 
> >    x86-64: Disable local APIC timer use on AMD systems with C1E
> > 
> >    It's not necessary for 2.6.23 and actually kills the box that it's supposed to fix. ]
> > 
> > 2) 2.6.23-rc8 w/ the "x86-64: Disable local APIC timer use on AMD systems with C1E"
> >    patch applied behaves like the current -git
> > 
> > 3) 2.6.23-rc8 w/o this patch doesn't boot with either "noapictimer" _or_
> 
> OK, this explains 2) and 3). I just looked into the code and the logic
> vs. noapictimer on SMP is completely broken.
> 
> On i386 the noapictimer option not only disables the local APIC timer,
> it also registers the CPUs for broadcasting via IPI on SMP systems. 
> 
> The x8664 code uses the broadcast only when the local apic timer is
> active, i.e. "noapictimer" is not on the command line. This defeats the
> whole purpose of "noapictimer". It should be there to make boxen work,
> where the local APIC timer actually has a hardware problem, e.g. the
> nx6325.
> 
> The current implementation of x86_64 only fixes the ACPI c-states
> related problem where the APIC timer stops in C3(2), nothing else.
> 
> On nx6325 and other AMD X2 equipped systems which have the C1E enabled
> we run into the following:
> 
> PIT keeps jiffies (and the system) running, but the local APIC timer
> interrupts can get out of sync due to this C1E effect. 
> 
> I don't think this is a critical problem, but it is wrong nevertheless.
> 
> I think it's safe to revert the C1E patch and postpone the fix to the
> clock events conversion.
> 
> >   "apicmaintimer"
> 
> on your box is not going to work. See the C1E patch. "apicmaintimer"
> switches off PIT and then waits for ever for the local APIC timer
> interrupts.
> 
> > 4) 2.6.22 behaves like 2.6.23-rc8
> 
> No surprise
> 
> > 5) 2.6.23-rc8 with (adjusted) patch-2.6.23-rc7-hrt1.patch boots only with
> >    "noapictimer"
> > 
> > 6) 2.6.23-rc8 with (adjusted) patch-2.6.23-rc7-hrt1.patch and with the
> >    "x86-64: Disable local APIC timer use on AMD systems with C1E" patch boots
> >    without any extra command line options
> 
> That's consistent behaviour.
> 
> > Tested for a couple of times with each kernel, the results seem to be
> > reproducible 100% of the time.
> 
> Thanks for going through this debug marathon.

No big deal.  I'm glad that you've found what's up.

Well, we still have the "CPU hotplug during suspend w/ the hrt patch" problem
to debug ... ;-)

Greetings,
Rafael
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