[PARISC] remove halftick and copy clocktick to local var (gcc can optimize usage)
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
bed583f76e
commit
6b799d9222
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@ -33,7 +33,6 @@
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#include <linux/timex.h>
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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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@ -48,6 +47,9 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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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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/* gcc can optimize for "read-only" case with a local clocktick */
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unsigned long local_ct = clocktick;
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profile_tick(CPU_PROFILING, regs);
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/* Initialize next_tick to the expected tick time. */
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@ -74,8 +76,16 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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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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if (likely(cycles_elapsed < local_ct)) {
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/* ticks_elapsed = 1 -- We already assumed one tick elapsed. */
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cycles_remainder = cycles_elapsed;
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} else {
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/* more than one tick elapsed. Do "expensive" math. */
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ticks_elapsed += cycles_elapsed / local_ct;
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/* Faster version of "remainder = elapsed % clocktick" */
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cycles_remainder = cycles_elapsed - (ticks_elapsed * local_ct);
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}
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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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@ -86,14 +96,12 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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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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printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
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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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@ -101,12 +109,19 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
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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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next_tick = now + (local_ct - cycles_remainder);
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/* Skip one clocktick on purpose if we are likely to miss next_tick.
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* We'll catch what we missed on the tick after that.
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* We should never need 0x1000 cycles to read CR16, calc the
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* new next_tick, then write CR16 back. */
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if (!((local_ct - cycles_remainder) >> 12))
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next_tick += local_ct;
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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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mtctl(next_tick, 16);
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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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@ -169,35 +184,37 @@ gettimeoffset (void)
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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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unsigned long cpuid = smp_processor_id();
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unsigned long local_ct = clocktick;
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next_tick = cpu_data[smp_processor_id()].it_value;
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next_tick = cpu_data[cpuid].it_value;
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now = mfctl(16); /* Read the hardware interval timer. */
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prev_tick = next_tick - clocktick;
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prev_tick = next_tick - local_ct;
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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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* ones complement is off-by-one. Don't care.
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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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if (elapsed_cycles > (HZ * local_ct)) {
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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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elapsed_cycles, prev_tick, now, next_tick, local_ct);
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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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usec += local_ct * (jiffies - wall_jiffies);
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return usec;
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#else
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return 0;
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@ -290,7 +307,6 @@ void __init time_init(void)
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static struct pdc_tod tod_data;
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clocktick = (100 * PAGE0->mem_10msec) / HZ;
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halftick = clocktick / 2;
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start_cpu_itimer(); /* get CPU 0 started */
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