[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
Matthew Wilcox
parent
65ee8f0a7f
commit
bed583f76e
1 changed files with 96 additions and 44 deletions
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@ -32,8 +32,8 @@
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#include <linux/timex.h>
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static long clocktick __read_mostly; /* timer cycles per tick */
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static long halftick __read_mostly;
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static unsigned long clocktick __read_mostly; /* timer cycles per tick */
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static unsigned long halftick __read_mostly;
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#ifdef CONFIG_SMP
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extern void smp_do_timer(struct pt_regs *regs);
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@ -41,34 +41,77 @@ extern void smp_do_timer(struct pt_regs *regs);
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irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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{
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long now;
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long next_tick;
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int nticks;
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unsigned long now;
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unsigned long next_tick;
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unsigned long cycles_elapsed;
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unsigned long cycles_remainder;
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unsigned long ticks_elapsed = 1; /* at least one elapsed */
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int cpu = smp_processor_id();
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profile_tick(CPU_PROFILING, regs);
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now = mfctl(16);
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/* initialize next_tick to time at last clocktick */
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/* Initialize next_tick to the expected tick time. */
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next_tick = cpu_data[cpu].it_value;
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/* since time passes between the interrupt and the mfctl()
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* above, it is never true that last_tick + clocktick == now. If we
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* never miss a clocktick, we could set next_tick = last_tick + clocktick
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* but maybe we'll miss ticks, hence the loop.
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*
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* Variables are *signed*.
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/* Get current interval timer.
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* CR16 reads as 64 bits in CPU wide mode.
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* CR16 reads as 32 bits in CPU narrow mode.
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*/
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now = mfctl(16);
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nticks = 0;
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while((next_tick - now) < halftick) {
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next_tick += clocktick;
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nticks++;
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cycles_elapsed = now - next_tick;
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/* Determine how much time elapsed. */
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if (now < next_tick) {
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/* Scenario 2: CR16 wrapped after clock tick.
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* 1's complement will give us the "elapse cycles".
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*
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* This "cr16 wrapped" cruft is primarily for 32-bit kernels.
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* So think "unsigned long is u32" when reading the code.
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* And yes, of course 64-bit will someday wrap, but only
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* every 198841 days on a 1GHz machine.
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*/
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cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */
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}
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ticks_elapsed += cycles_elapsed / clocktick;
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cycles_remainder = cycles_elapsed % clocktick;
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/* Can we differentiate between "early CR16" (aka Scenario 1) and
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* "long delay" (aka Scenario 3)? I don't think so.
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*
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* We expected timer_interrupt to be delivered at least a few hundred
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* cycles after the IT fires. But it's arbitrary how much time passes
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* before we call it "late". I've picked one second.
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*/
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if (ticks_elapsed > HZ) {
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/* Scenario 3: very long delay? bad in any case */
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printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate"
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" ticks %ld cycles %lX rem %lX"
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" next/now %lX/%lX\n",
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cpu,
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ticks_elapsed, cycles_elapsed, cycles_remainder,
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next_tick, now );
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ticks_elapsed = 1; /* hack to limit damage in loop below */
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}
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/* Determine when (in CR16 cycles) next IT interrupt will fire.
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* We want IT to fire modulo clocktick even if we miss/skip some.
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* But those interrupts don't in fact get delivered that regularly.
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*/
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next_tick = now + (clocktick - cycles_remainder);
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/* Program the IT when to deliver the next interrupt. */
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/* Only bottom 32-bits of next_tick are written to cr16. */
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mtctl(next_tick, 16);
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cpu_data[cpu].it_value = next_tick;
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while (nticks--) {
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/* Now that we are done mucking with unreliable delivery of interrupts,
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* go do system house keeping.
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*/
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while (ticks_elapsed--) {
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#ifdef CONFIG_SMP
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smp_do_timer(regs);
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#else
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@ -121,21 +164,41 @@ gettimeoffset (void)
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* Once parisc-linux learns the cr16 difference between processors,
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* this could be made to work.
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*/
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long last_tick;
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long elapsed_cycles;
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unsigned long now;
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unsigned long prev_tick;
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unsigned long next_tick;
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unsigned long elapsed_cycles;
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unsigned long usec;
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/* it_value is the intended time of the next tick */
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last_tick = cpu_data[smp_processor_id()].it_value;
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next_tick = cpu_data[smp_processor_id()].it_value;
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now = mfctl(16); /* Read the hardware interval timer. */
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/* Subtract one tick and account for possible difference between
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* when we expected the tick and when it actually arrived.
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* (aka wall vs real)
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*/
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last_tick -= clocktick * (jiffies - wall_jiffies + 1);
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elapsed_cycles = mfctl(16) - last_tick;
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prev_tick = next_tick - clocktick;
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/* the precision of this math could be improved */
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return elapsed_cycles / (PAGE0->mem_10msec / 10000);
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/* Assume Scenario 1: "now" is later than prev_tick. */
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elapsed_cycles = now - prev_tick;
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if (now < prev_tick) {
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/* Scenario 2: CR16 wrapped!
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* 1's complement is close enough.
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*/
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elapsed_cycles = ~elapsed_cycles;
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}
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if (elapsed_cycles > (HZ * clocktick)) {
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/* Scenario 3: clock ticks are missing. */
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printk (KERN_CRIT "gettimeoffset(CPU %d): missing ticks!"
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"cycles %lX prev/now/next %lX/%lX/%lX clock %lX\n",
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cpuid,
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elapsed_cycles, prev_tick, now, next_tick, clocktick);
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}
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/* FIXME: Can we improve the precision? Not with PAGE0. */
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usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
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/* add in "lost" jiffies */
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usec += clocktick * (jiffies - wall_jiffies);
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return usec;
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#else
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return 0;
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#endif
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@ -146,6 +209,7 @@ do_gettimeofday (struct timeval *tv)
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{
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unsigned long flags, seq, usec, sec;
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/* Hold xtime_lock and adjust timeval. */
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do {
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seq = read_seqbegin_irqsave(&xtime_lock, flags);
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usec = gettimeoffset();
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@ -153,25 +217,13 @@ do_gettimeofday (struct timeval *tv)
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usec += (xtime.tv_nsec / 1000);
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} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
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if (unlikely(usec > LONG_MAX)) {
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/* This can happen if the gettimeoffset adjustment is
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* negative and xtime.tv_nsec is smaller than the
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* adjustment */
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printk(KERN_ERR "do_gettimeofday() spurious xtime.tv_nsec of %ld\n", usec);
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usec += USEC_PER_SEC;
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--sec;
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/* This should never happen, it means the negative
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* time adjustment was more than a second, so there's
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* something seriously wrong */
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BUG_ON(usec > LONG_MAX);
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}
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/* Move adjusted usec's into sec's. */
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while (usec >= USEC_PER_SEC) {
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usec -= USEC_PER_SEC;
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++sec;
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}
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/* Return adjusted result. */
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tv->tv_sec = sec;
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tv->tv_usec = usec;
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}
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