Nforce2, APIC, CPU Disconnect and setup_boot_APIC_clock()

[cheuche+lkml@free.fr]

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Hello all,

I once noticed there was a drift between the 8254 timer and the APIC
timer. With vanilla and -mm kernels, APIC timer is running faster. With
Ross' patches I noticed it was running slower, and the crashes go away.
I dig in that direction and found that with a APIC timer directly
programmed slower than calibrated, adding ~20 more bus cycles to the
counter, hangs disappear, at least during the tests (for a few minutes,
maybe they are made much rarer). I eventually disabled altogether the
APIC timer with the patchlet attached, and did an entire test (dumping
the whole hard drive to /dev/null with very high network and soundcard
activity), and it survived. I will continue to test, just to make
sure...

At least there is a way to get nforce2 + APIC + CPU disconnect and
actually have a cooler idle CPU. Side effects are no more LOC rising
counter in /proc/interrupts, no more nmi_watchdog=2 and if you work
around the bios acpi apic source override to get the timer on pin #0, no
more nmi_watchdog=1. This is of course not the best solution.

Now the experts may look why commenting out setup_boot_APIC_clock() in
APIC_init_uniprocessor() of arch/i386/kernel/apic.c works, and find a
better fix if any.

Mathieu

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--- arch/i386/kernel/apic.c.old	2004-02-13 16:13:39.000000000 +0100
+++ arch/i386/kernel/apic.c	2004-02-13 14:29:29.000000000 +0100
@@ -1198,7 +1198,7 @@
 		if (!skip_ioapic_setup && nr_ioapics)
 			setup_IO_APIC();
 #endif
-	setup_boot_APIC_clock();
+	/*setup_boot_APIC_clock();*/
 
 	return 0;
 }