[PATCH] x86_64: Allow to run main time keeping from the local APIC interrupt

Another piece from the no-idle-tick patch.

This can be enabled with the "apicmaintimer" option.

This is mainly useful when the PIT/HPET interrupt is unreliable.
Note there are some systems that are known to stop the APIC
timer in C3. For those it will never work, but this case
should be automatically detected.

It also only works with PM timer right now. When HPET is used
the way the main timer handler computes the delay doesn't work.

It should be a bit more efficient because there is one less
regular interrupt to process on the boot processor.

Requires earlier bugfix from Venkatesh

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 32 insertions, 2 deletions

diff --git a/arch/x86_64/kernel/apic.c b/arch/x86_64/kernel/apic.c
index 5d3c5b07b8db..14751dda7dcf 100644
--- a/arch/x86_64/kernel/apic.c
+++ b/arch/x86_64/kernel/apic.c
@@ -35,8 +35,11 @@
 #include <asm/mach_apic.h>
 #include <asm/nmi.h>
 #include <asm/idle.h>
+#include <asm/proto.h>
+#include <asm/timex.h>
 
 int apic_verbosity;
+int apic_runs_main_timer;
 
 int disable_apic_timer __initdata;
 
@@ -702,9 +705,17 @@ static void setup_APIC_timer(unsigned int clocks)
 			c2 |= inb_p(0x40) << 8;
 		} while (c2 - c1 < 300);
 	}
-
 	__setup_APIC_LVTT(clocks);
-
+	/* Turn off PIT interrupt if we use APIC timer as main timer.
+	   Only works with the PM timer right now
+	   TBD fix it for HPET too. */
+	if (vxtime.mode == VXTIME_PMTMR &&
+		smp_processor_id() == boot_cpu_id &&
+		apic_runs_main_timer == 1 &&
+		!cpu_isset(boot_cpu_id, timer_interrupt_broadcast_ipi_mask)) {
+		stop_timer_interrupt();
+		apic_runs_main_timer++;
+	}
 	local_irq_restore(flags);
 }
 
@@ -872,6 +883,8 @@ void smp_local_timer_interrupt(struct pt_regs *regs)
 #ifdef CONFIG_SMP
 	update_process_times(user_mode(regs));
 #endif
+	if (apic_runs_main_timer > 1 && smp_processor_id() == boot_cpu_id)
+		main_timer_handler(regs);
 	/*
 	 * We take the 'long' return path, and there every subsystem
 	 * grabs the appropriate locks (kernel lock/ irq lock).
@@ -1081,10 +1094,27 @@ static __init int setup_nolapic(char *str)
 
 static __init int setup_noapictimer(char *str) 
 { 
+	if (str[0] != ' ' && str[0] != 0)
+		return -1;
 	disable_apic_timer = 1;
 	return 0;
 } 
 
+static __init int setup_apicmaintimer(char *str)
+{
+	apic_runs_main_timer = 1;
+	nohpet = 1;
+	return 0;
+}
+__setup("apicmaintimer", setup_apicmaintimer);
+
+static __init int setup_noapicmaintimer(char *str)
+{
+	apic_runs_main_timer = -1;
+	return 0;
+}
+__setup("noapicmaintimer", setup_noapicmaintimer);
+
 /* dummy parsing: see setup.c */
 
 __setup("disableapic", setup_disableapic);