From ab9b32ee626e9b6df4ce2560a70ae15e62423cf4 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Sun, 26 Feb 2006 04:18:52 +0100 Subject: [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 Signed-off-by: Linus Torvalds --- Documentation/x86_64/boot-options.txt | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation') diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt index 153740f460a6..1921353259ae 100644 --- a/Documentation/x86_64/boot-options.txt +++ b/Documentation/x86_64/boot-options.txt @@ -52,6 +52,10 @@ APICs apicmaintimer. Useful when your PIT timer is totally broken. + disable_8254_timer / enable_8254_timer + Enable interrupt 0 timer routing over the 8254 in addition to over + the IO-APIC. The kernel tries to set a sensible default. + Early Console syntax: earlyprintk=vga -- cgit v1.2.1