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-rw-r--r--arch/parisc/kernel/time.c90
1 files changed, 54 insertions, 36 deletions
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index d4dd05674c6..a79c6f9e7e2 100644
--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -56,9 +56,9 @@ static unsigned long clocktick __read_mostly; /* timer cycles per tick */
*/
irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
{
- unsigned long now;
+ unsigned long now, now2;
unsigned long next_tick;
- unsigned long cycles_elapsed, ticks_elapsed;
+ unsigned long cycles_elapsed, ticks_elapsed = 1;
unsigned long cycles_remainder;
unsigned int cpu = smp_processor_id();
struct cpuinfo_parisc *cpuinfo = &per_cpu(cpu_data, cpu);
@@ -71,44 +71,24 @@ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
/* Initialize next_tick to the expected tick time. */
next_tick = cpuinfo->it_value;
- /* Get current interval timer.
- * CR16 reads as 64 bits in CPU wide mode.
- * CR16 reads as 32 bits in CPU narrow mode.
- */
+ /* Get current cycle counter (Control Register 16). */
now = mfctl(16);
cycles_elapsed = now - next_tick;
- if ((cycles_elapsed >> 5) < cpt) {
+ if ((cycles_elapsed >> 6) < cpt) {
/* use "cheap" math (add/subtract) instead
* of the more expensive div/mul method
*/
cycles_remainder = cycles_elapsed;
- ticks_elapsed = 1;
while (cycles_remainder > cpt) {
cycles_remainder -= cpt;
ticks_elapsed++;
}
} else {
+ /* TODO: Reduce this to one fdiv op */
cycles_remainder = cycles_elapsed % cpt;
- ticks_elapsed = 1 + cycles_elapsed / cpt;
- }
-
- /* Can we differentiate between "early CR16" (aka Scenario 1) and
- * "long delay" (aka Scenario 3)? I don't think so.
- *
- * We expected timer_interrupt to be delivered at least a few hundred
- * cycles after the IT fires. But it's arbitrary how much time passes
- * before we call it "late". I've picked one second.
- */
- if (unlikely(ticks_elapsed > HZ)) {
- /* Scenario 3: very long delay? bad in any case */
- printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
- " cycles %lX rem %lX "
- " next/now %lX/%lX\n",
- cpu,
- cycles_elapsed, cycles_remainder,
- next_tick, now );
+ ticks_elapsed += cycles_elapsed / cpt;
}
/* convert from "division remainder" to "remainder of clock tick" */
@@ -122,18 +102,56 @@ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id)
cpuinfo->it_value = next_tick;
- /* Skip one clocktick on purpose if we are likely to miss next_tick.
- * We want to avoid the new next_tick being less than CR16.
- * If that happened, itimer wouldn't fire until CR16 wrapped.
- * We'll catch the tick we missed on the tick after that.
+ /* Program the IT when to deliver the next interrupt.
+ * Only bottom 32-bits of next_tick are writable in CR16!
*/
- if (!(cycles_remainder >> 13))
- next_tick += cpt;
-
- /* Program the IT when to deliver the next interrupt. */
- /* Only bottom 32-bits of next_tick are written to cr16. */
mtctl(next_tick, 16);
+ /* Skip one clocktick on purpose if we missed next_tick.
+ * The new CR16 must be "later" than current CR16 otherwise
+ * itimer would not fire until CR16 wrapped - e.g 4 seconds
+ * later on a 1Ghz processor. We'll account for the missed
+ * tick on the next timer interrupt.
+ *
+ * "next_tick - now" will always give the difference regardless
+ * if one or the other wrapped. If "now" is "bigger" we'll end up
+ * with a very large unsigned number.
+ */
+ now2 = mfctl(16);
+ if (next_tick - now2 > cpt)
+ mtctl(next_tick+cpt, 16);
+
+#if 1
+/*
+ * GGG: DEBUG code for how many cycles programming CR16 used.
+ */
+ if (unlikely(now2 - now > 0x3000)) /* 12K cycles */
+ printk (KERN_CRIT "timer_interrupt(CPU %d): SLOW! 0x%lx cycles!"
+ " cyc %lX rem %lX "
+ " next/now %lX/%lX\n",
+ cpu, now2 - now, cycles_elapsed, cycles_remainder,
+ next_tick, now );
+#endif
+
+ /* Can we differentiate between "early CR16" (aka Scenario 1) and
+ * "long delay" (aka Scenario 3)? I don't think so.
+ *
+ * Timer_interrupt will be delivered at least a few hundred cycles
+ * after the IT fires. But it's arbitrary how much time passes
+ * before we call it "late". I've picked one second.
+ *
+ * It's important NO printk's are between reading CR16 and
+ * setting up the next value. May introduce huge variance.
+ */
+ if (unlikely(ticks_elapsed > HZ)) {
+ /* Scenario 3: very long delay? bad in any case */
+ printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
+ " cycles %lX rem %lX "
+ " next/now %lX/%lX\n",
+ cpu,
+ cycles_elapsed, cycles_remainder,
+ next_tick, now );
+ }
/* Done mucking with unreliable delivery of interrupts.
* Go do system house keeping.
@@ -173,7 +191,7 @@ EXPORT_SYMBOL(profile_pc);
/* clock source code */
-static cycle_t read_cr16(void)
+static cycle_t read_cr16(struct clocksource *cs)
{
return get_cycles();
}