x86-64: Disable local APIC timer use on AMD systems with C1E

commit 3556ddfa9284a86a59a9b78fe5894430f6ab4eef titled

 [PATCH] x86-64: Disable local APIC timer use on AMD systems with C1E

solves a problem with AMD dual core laptops e.g. HP nx6325 (Turion 64
X2) with C1E enabled:

When both cores go into idle at the same time, then the system switches
into C1E state, which is basically the same as C3. This stops the local
apic timer.

This was debugged right after the dyntick merge on i386 and despite the
patch title it fixes only the 32 bit path.

x86_64 is still missing this fix. It seems that mainline is not really
affected by this issue, as the PIT is running and keeps jiffies
incrementing, but that's just waiting for trouble.

-mm suffers from this problem due to the x86_64 high resolution timer
patches.

This is a quick and dirty port of the i386 code to x86_64.

I spent quite a time with Rafael to debug the -mm / hrt wreckage until
someone pointed us to this. I really had forgotten that we debugged this
half a year ago already.

Sigh, is it just me or is there something yelling arch/x86 into my ear?

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/asm-x86_64/apic.h b/include/asm-x86_64/apic.h
index 85125ef..e458020 100644
--- a/include/asm-x86_64/apic.h
+++ b/include/asm-x86_64/apic.h
@@ -20,6 +20,7 @@ extern int apic_verbosity;
 extern int apic_runs_main_timer;
 extern int ioapic_force;
 extern int apic_mapped;
+extern int disable_apic_timer;
 
 /*
  * Define the default level of output to be very little