[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, 38 insertions, 7 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index f8c47c688443..91a448a86ebd 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -51,7 +51,7 @@ extern int using_apic_timer;
 DEFINE_SPINLOCK(rtc_lock);
 DEFINE_SPINLOCK(i8253_lock);
 
-static int nohpet __initdata = 0;
+int nohpet __initdata = 0;
 static int notsc __initdata = 0;
 
 #undef HPET_HACK_ENABLE_DANGEROUS
@@ -345,7 +345,7 @@ static noinline void handle_lost_ticks(int lost, struct pt_regs *regs)
 #endif
 }
 
-static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+void main_timer_handler(struct pt_regs *regs)
 {
         static unsigned long rtc_update = 0;
         unsigned long tsc;
@@ -458,12 +458,17 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
         }
  
         write_sequnlock(&xtime_lock);
+}
 
+static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
+{
+        if (apic_runs_main_timer > 1)
+                return IRQ_HANDLED;
+        main_timer_handler(regs);
 #ifdef CONFIG_X86_LOCAL_APIC
         if (using_apic_timer)
                 smp_send_timer_broadcast_ipi();
 #endif
-
         return IRQ_HANDLED;
 }
 
@@ -843,17 +848,43 @@ static int hpet_reenable(void)
         return hpet_timer_stop_set_go(hpet_tick);
 }
 
-void __init pit_init(void)
+#define PIT_MODE 0x43
+#define PIT_CH0  0x40
+
+static void __init __pit_init(int val, u8 mode)
 {
         unsigned long flags;
 
         spin_lock_irqsave(&i8253_lock, flags);
-        outb_p(0x34, 0x43);             /* binary, mode 2, LSB/MSB, ch 0 */
-        outb_p(LATCH & 0xff, 0x40);     /* LSB */
-        outb_p(LATCH >> 8, 0x40);       /* MSB */
+        outb_p(mode, PIT_MODE);
+        outb_p(val & 0xff, PIT_CH0);    /* LSB */
+        outb_p(val >> 8, PIT_CH0);      /* MSB */
         spin_unlock_irqrestore(&i8253_lock, flags);
 }
 
+void __init pit_init(void)
+{
+        __pit_init(LATCH, 0x34); /* binary, mode 2, LSB/MSB, ch 0 */
+}
+
+void __init pit_stop_interrupt(void)
+{
+        __pit_init(0, 0x30); /* mode 0 */
+}
+
+void __init stop_timer_interrupt(void)
+{
+        char *name;
+        if (vxtime.hpet_address) {
+                name = "HPET";
+                hpet_timer_stop_set_go(0);
+        } else {
+                name = "PIT";
+                pit_stop_interrupt();
+        }
+        printk(KERN_INFO "timer: %s interrupt stopped.\n", name);
+}
+
 int __init time_setup(char *str)
 {
         report_lost_ticks = 1;