[PARISC] Rewrite timer_interrupt() and gettimeoffset() using "unsigned" math.
It's just a bit easier to follow and timer code is complex enough.
So far, only tested on A500-5x (64-bit SMP), ie: gettimeoffset() code
hasn't been tested at all.
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 47831c2..fd425e1 100644
--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -32,8 +32,8 @@
#include <linux/timex.h>
-static long clocktick __read_mostly; /* timer cycles per tick */
-static long halftick __read_mostly;
+static unsigned long clocktick __read_mostly; /* timer cycles per tick */
+static unsigned long halftick __read_mostly;
#ifdef CONFIG_SMP
extern void smp_do_timer(struct pt_regs *regs);
@@ -41,34 +41,77 @@
irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
- long now;
- long next_tick;
- int nticks;
+ 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();
profile_tick(CPU_PROFILING, regs);
- now = mfctl(16);
- /* initialize next_tick to time at last clocktick */
+ /* Initialize next_tick to the expected tick time. */
next_tick = cpu_data[cpu].it_value;
- /* since time passes between the interrupt and the mfctl()
- * above, it is never true that last_tick + clocktick == now. If we
- * never miss a clocktick, we could set next_tick = last_tick + clocktick
- * but maybe we'll miss ticks, hence the loop.
- *
- * Variables are *signed*.
+ /* Get current interval timer.
+ * CR16 reads as 64 bits in CPU wide mode.
+ * CR16 reads as 32 bits in CPU narrow mode.
*/
+ now = mfctl(16);
- nticks = 0;
- while((next_tick - now) < halftick) {
- next_tick += clocktick;
- nticks++;
+ 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.
+ */
+ cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */
}
+
+ ticks_elapsed += cycles_elapsed / clocktick;
+ cycles_remainder = cycles_elapsed % clocktick;
+
+ /* 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 (ticks_elapsed > HZ) {
+ /* Scenario 3: very long delay? bad in any case */
+ printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate"
+ " ticks %ld cycles %lX rem %lX"
+ " next/now %lX/%lX\n",
+ cpu,
+ ticks_elapsed, cycles_elapsed, cycles_remainder,
+ next_tick, now );
+
+ ticks_elapsed = 1; /* hack to limit damage in loop below */
+ }
+
+
+ /* 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 + (clocktick - cycles_remainder);
+
+ /* Program the IT when to deliver the next interrupt. */
+ /* Only bottom 32-bits of next_tick are written to cr16. */
mtctl(next_tick, 16);
cpu_data[cpu].it_value = next_tick;
- while (nticks--) {
+ /* Now that we are done mucking with unreliable delivery of interrupts,
+ * go do system house keeping.
+ */
+ while (ticks_elapsed--) {
#ifdef CONFIG_SMP
smp_do_timer(regs);
#else
@@ -121,21 +164,41 @@
* Once parisc-linux learns the cr16 difference between processors,
* this could be made to work.
*/
- long last_tick;
- long elapsed_cycles;
+ unsigned long now;
+ unsigned long prev_tick;
+ unsigned long next_tick;
+ unsigned long elapsed_cycles;
+ unsigned long usec;
- /* it_value is the intended time of the next tick */
- last_tick = cpu_data[smp_processor_id()].it_value;
+ next_tick = cpu_data[smp_processor_id()].it_value;
+ now = mfctl(16); /* Read the hardware interval timer. */
- /* Subtract one tick and account for possible difference between
- * when we expected the tick and when it actually arrived.
- * (aka wall vs real)
- */
- last_tick -= clocktick * (jiffies - wall_jiffies + 1);
- elapsed_cycles = mfctl(16) - last_tick;
+ prev_tick = next_tick - clocktick;
- /* the precision of this math could be improved */
- return elapsed_cycles / (PAGE0->mem_10msec / 10000);
+ /* Assume Scenario 1: "now" is later than prev_tick. */
+ elapsed_cycles = now - prev_tick;
+
+ if (now < prev_tick) {
+ /* Scenario 2: CR16 wrapped!
+ * 1's complement is close enough.
+ */
+ elapsed_cycles = ~elapsed_cycles;
+ }
+
+ if (elapsed_cycles > (HZ * clocktick)) {
+ /* 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, clocktick);
+ }
+
+ /* FIXME: Can we improve the precision? Not with PAGE0. */
+ usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
+
+ /* add in "lost" jiffies */
+ usec += clocktick * (jiffies - wall_jiffies);
+ return usec;
#else
return 0;
#endif
@@ -146,6 +209,7 @@
{
unsigned long flags, seq, usec, sec;
+ /* Hold xtime_lock and adjust timeval. */
do {
seq = read_seqbegin_irqsave(&xtime_lock, flags);
usec = gettimeoffset();
@@ -153,25 +217,13 @@
usec += (xtime.tv_nsec / 1000);
} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
- if (unlikely(usec > LONG_MAX)) {
- /* This can happen if the gettimeoffset adjustment is
- * negative and xtime.tv_nsec is smaller than the
- * adjustment */
- printk(KERN_ERR "do_gettimeofday() spurious xtime.tv_nsec of %ld\n", usec);
- usec += USEC_PER_SEC;
- --sec;
- /* This should never happen, it means the negative
- * time adjustment was more than a second, so there's
- * something seriously wrong */
- BUG_ON(usec > LONG_MAX);
- }
-
-
+ /* Move adjusted usec's into sec's. */
while (usec >= USEC_PER_SEC) {
usec -= USEC_PER_SEC;
++sec;
}
+ /* Return adjusted result. */
tv->tv_sec = sec;
tv->tv_usec = usec;
}