[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>
This commit is contained in:
Grant Grundler 2006-09-08 23:29:22 -07:00 committed by Matthew Wilcox
parent 65ee8f0a7f
commit bed583f76e

View file

@ -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 @@ extern void smp_do_timer(struct pt_regs *regs);
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 @@ gettimeoffset (void)
* 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 @@ do_gettimeofday (struct timeval *tv)
{
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 @@ do_gettimeofday (struct timeval *tv)
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;
}