[PARISC] Further updates to timer_interrupt()
This version (relative to the current tree):
o eliminates "while (ticks_elapsed)" loop. It's not needed.
o drop "ticks_elapsed" completely from timer_interrupt().
o Estimates elapsed cycles (based on HZ) to see which kind of
math we want to use to calculate "cycles_remainder".
o Fixes a bug where we would loose a tick if we decided
we wanted to skip one interrupt.
Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index c43e847..9d642d8 100644
--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -43,12 +43,11 @@
unsigned long now;
unsigned long next_tick;
unsigned long cycles_elapsed;
- unsigned long cycles_remainder;
- unsigned long ticks_elapsed = 1; /* at least one elapsed */
- int cpu = smp_processor_id();
+ unsigned long cycles_remainder;
+ unsigned int cpu = smp_processor_id();
/* gcc can optimize for "read-only" case with a local clocktick */
- unsigned long local_ct = clocktick;
+ unsigned long cpt = clocktick;
profile_tick(CPU_PROFILING, regs);
@@ -63,28 +62,16 @@
cycles_elapsed = now - next_tick;
- /* Determine how much time elapsed. */
- if (now < next_tick) {
- /* Scenario 2: CR16 wrapped after clock tick.
- * 1's complement will give us the "elapse cycles".
- *
- * This "cr16 wrapped" cruft is primarily for 32-bit kernels.
- * So think "unsigned long is u32" when reading the code.
- * And yes, of course 64-bit will someday wrap, but only
- * every 198841 days on a 1GHz machine.
+ if ((cycles_elapsed >> 5) < cpt) {
+ /* use "cheap" math (add/subtract) instead
+ * of the more expensive div/mul method
*/
- cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */
- }
-
- if (likely(cycles_elapsed < local_ct)) {
- /* ticks_elapsed = 1 -- We already assumed one tick elapsed. */
cycles_remainder = cycles_elapsed;
+ while (cycles_remainder > cpt) {
+ cycles_remainder -= cpt;
+ }
} else {
- /* more than one tick elapsed. Do "expensive" math. */
- ticks_elapsed += cycles_elapsed / local_ct;
-
- /* Faster version of "remainder = elapsed % clocktick" */
- cycles_remainder = cycles_elapsed - (ticks_elapsed * local_ct);
+ cycles_remainder = cycles_elapsed % cpt;
}
/* Can we differentiate between "early CR16" (aka Scenario 1) and
@@ -94,51 +81,65 @@
* cycles after the IT fires. But it's arbitrary how much time passes
* before we call it "late". I've picked one second.
*/
- if (ticks_elapsed > HZ) {
+/* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
+#if HZ == 1000
+ if (cycles_elapsed > (cpt << 10) )
+#elif HZ == 250
+ if (cycles_elapsed > (cpt << 8) )
+#elif HZ == 100
+ if (cycles_elapsed > (cpt << 7) )
+#else
+#warn WTF is HZ set to anyway?
+ if (cycles_elapsed > (HZ * cpt) )
+#endif
+ {
/* Scenario 3: very long delay? bad in any case */
printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
- " ticks %ld cycles %lX rem %lX"
+ " cycles %lX rem %lX "
" next/now %lX/%lX\n",
cpu,
- ticks_elapsed, cycles_elapsed, cycles_remainder,
+ cycles_elapsed, cycles_remainder,
next_tick, now );
}
+ /* convert from "division remainder" to "remainder of clock tick" */
+ cycles_remainder = cpt - cycles_remainder;
/* Determine when (in CR16 cycles) next IT interrupt will fire.
* We want IT to fire modulo clocktick even if we miss/skip some.
* But those interrupts don't in fact get delivered that regularly.
*/
- next_tick = now + (local_ct - cycles_remainder);
+ next_tick = now + cycles_remainder;
+
+ cpu_data[cpu].it_value = next_tick;
/* Skip one clocktick on purpose if we are likely to miss next_tick.
- * We'll catch what we missed on the tick after that.
- * We should never need 0x1000 cycles to read CR16, calc the
- * new next_tick, then write CR16 back. */
- if (!((local_ct - cycles_remainder) >> 12))
- next_tick += local_ct;
+ * 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.
+ */
+ 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. */
- cpu_data[cpu].it_value = next_tick;
mtctl(next_tick, 16);
- /* Now that we are done mucking with unreliable delivery of interrupts,
- * go do system house keeping.
+
+ /* Done mucking with unreliable delivery of interrupts.
+ * Go do system house keeping.
*/
- while (ticks_elapsed--) {
#ifdef CONFIG_SMP
- smp_do_timer(regs);
+ smp_do_timer(regs);
#else
- update_process_times(user_mode(regs));
+ update_process_times(user_mode(regs));
#endif
- if (cpu == 0) {
- write_seqlock(&xtime_lock);
- do_timer(1);
- write_sequnlock(&xtime_lock);
- }
+ if (cpu == 0) {
+ write_seqlock(&xtime_lock);
+ do_timer(regs);
+ write_sequnlock(&xtime_lock);
}
-
+
/* check soft power switch status */
if (cpu == 0 && !atomic_read(&power_tasklet.count))
tasklet_schedule(&power_tasklet);
@@ -164,14 +165,12 @@
EXPORT_SYMBOL(profile_pc);
-/*** converted from ia64 ***/
/*
* Return the number of micro-seconds that elapsed since the last
* update to wall time (aka xtime). The xtime_lock
* must be at least read-locked when calling this routine.
*/
-static inline unsigned long
-gettimeoffset (void)
+static inline unsigned long gettimeoffset (void)
{
#ifndef CONFIG_SMP
/*
@@ -185,36 +184,40 @@
unsigned long elapsed_cycles;
unsigned long usec;
unsigned long cpuid = smp_processor_id();
- unsigned long local_ct = clocktick;
+ unsigned long cpt = clocktick;
next_tick = cpu_data[cpuid].it_value;
now = mfctl(16); /* Read the hardware interval timer. */
- prev_tick = next_tick - local_ct;
+ prev_tick = next_tick - cpt;
/* Assume Scenario 1: "now" is later than prev_tick. */
elapsed_cycles = now - prev_tick;
- if (now < prev_tick) {
- /* Scenario 2: CR16 wrapped!
- * ones complement is off-by-one. Don't care.
- */
- elapsed_cycles = ~elapsed_cycles;
- }
-
- if (elapsed_cycles > (HZ * local_ct)) {
+/* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
+#if HZ == 1000
+ if (elapsed_cycles > (cpt << 10) )
+#elif HZ == 250
+ if (elapsed_cycles > (cpt << 8) )
+#elif HZ == 100
+ if (elapsed_cycles > (cpt << 7) )
+#else
+#warn WTF is HZ set to anyway?
+ if (elapsed_cycles > (HZ * cpt) )
+#endif
+ {
/* Scenario 3: clock ticks are missing. */
- printk (KERN_CRIT "gettimeoffset(CPU %d): missing ticks!"
- "cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
- cpuid,
- elapsed_cycles, prev_tick, now, next_tick, local_ct);
+ printk (KERN_CRIT "gettimeoffset(CPU %ld): missing %ld ticks!"
+ " cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
+ cpuid, elapsed_cycles / cpt,
+ elapsed_cycles, prev_tick, now, next_tick, cpt);
}
/* FIXME: Can we improve the precision? Not with PAGE0. */
usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
/* add in "lost" jiffies */
- usec += local_ct * (jiffies - wall_jiffies);
+ usec += cpt * (jiffies - wall_jiffies);
return usec;
#else
return 0;