kernel-ark/Documentation/x86_64
Andi Kleen ab9b32ee62 [PATCH] x86_64: Better ATI timer fix
The previous experiment for using apicmaintimer on ATI systems didn't
work out very well.  In particular laptops with C2/C3 support often
don't let it tick during idle, which makes it useless.  There were also
some other bugs that made the apicmaintimer often not used at all.

I tried some other experiments - running timer over RTC and some other
things but they didn't really work well neither.

I rechecked the specs now and it turns out this simple change is
actually enough to avoid the double ticks on the ATI systems.  We just
turn off IRQ 0 in the 8254 and only route it directly using the IO-APIC.

I tested it on a few ATI systems and it worked there.  In fact it worked
on all chipsets (NVidia, Intel, AMD, ATI) I tried it on.

According to the ACPI spec routing should always work through the
IO-APIC so I think it's the correct thing to do anyways (and most of the
old gunk in check_timer should be thrown away for x86-64).

But for 2.6.16 it's best to do a fairly minimal change:
 - Use the known to be working everywhere-but-ATI IRQ0 both over 8254
   and IO-APIC setup everywhere
 - Except on ATI disable IRQ0 in the 8254
 - Remove the code to select apicmaintimer on ATI chipsets
 - Add some boot options to allow to override this (just paranoia)

In 2.6.17 I hope to switch the default over to this for everybody.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-02-26 09:53:31 -08:00
..
boot-options.txt [PATCH] x86_64: Better ATI timer fix 2006-02-26 09:53:31 -08:00
cpu-hotplug-spec [PATCH] x86_64: Add documentation for CPU hotplug ACPI extension 2006-01-11 19:01:11 -08:00
mm.txt [PATCH] x86_64: Some clarifications for Documention/x86_64/mm.txt 2005-11-14 19:55:15 -08:00