linux/arch/x86_64
Linus Torvalds f7f847b015 Revert "x86-64: Disable local APIC timer use on AMD systems with C1E"
This reverts commit e66485d747, since
Rafael Wysocki noticed that the change only works for his in -mm, not in
mainline (and that both "noapictimer" _and_ "apicmaintimer" are broken
on his hardware, but that's apparently not a regression, just a symptom
of the same issue that causes the automatic apic timer disable to not
work).

It turns out that it really doesn't work correctly on x86-64, since
x86-64 doesn't use the generic clock events for timers yet.

Thanks to Rafal for testing, and here's the ugly details on x86-64 as
per Thomas:

  "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 x86-64 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."

On further reflection, Thomas noted:

   "It's even worse than I thought on the first check:

    "noapictimer" on the command line of an SMP box prevents _ONLY_ the
    boot CPU apic timer from being used.  But the secondary CPU is still
    unconditionally setting up the APIC timer and uses the non
    calibrated variable calibration_result, which is of course 0, to
    setup the APIC timer.  Wreckage guaranteed."

so we'll just have to wait for the x86 merge to hopefully fix this up
for x86-64.

Tested-and-requested-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-09-26 15:43:41 -07:00
..
boot x86_64: Early segment setup for VT 2007-08-11 15:58:13 -07:00
crypto [CRYPTO] api: Get rid of flags argument to setkey 2006-09-21 11:41:02 +10:00
ia32 x86_64: Zero extend all registers after ptrace in 32bit entry path. 2007-09-21 09:52:07 -07:00
kernel Revert "x86-64: Disable local APIC timer use on AMD systems with C1E" 2007-09-26 15:43:41 -07:00
lib Do not replace whole memcpy in apply alternatives 2007-08-12 01:42:37 -07:00
mm x86-64: page faults from user mode are always user faults 2007-09-19 11:37:14 -07:00
oprofile [PATCH] Move Kprobes and Oprofile to "Instrumentation Support" menu 2005-11-07 07:53:35 -08:00
pci x86: Work around mmio config space quirk on AMD Fam10h 2007-08-11 15:58:12 -07:00
vdso x86_64: Add missing mask operation to vdso 2007-09-12 09:28:06 -07:00
defconfig PM: Fix dependencies of CONFIG_SUSPEND and CONFIG_HIBERNATION 2007-08-31 01:42:22 -07:00
Kconfig Revert "x86_64: Quicklist support for x86_64" 2007-09-21 12:09:41 -07:00
Kconfig.debug Allow DEBUG_RODATA and KPROBES to co-exist 2007-06-21 16:02:50 -07:00
Makefile x86_64: Check for .cfi_rel_offset in CFI probe 2007-08-18 10:25:25 -07:00