diff options
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/parisc/kernel/time.c | 46 |
1 files changed, 31 insertions, 15 deletions
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c index fd425e1abe66..c43e847a4b8f 100644 --- a/arch/parisc/kernel/time.c +++ b/arch/parisc/kernel/time.c @@ -33,7 +33,6 @@ #include <linux/timex.h> 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); @@ -48,6 +47,9 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) unsigned long ticks_elapsed = 1; /* at least one elapsed */ int cpu = smp_processor_id(); + /* gcc can optimize for "read-only" case with a local clocktick */ + unsigned long local_ct = clocktick; + profile_tick(CPU_PROFILING, regs); /* Initialize next_tick to the expected tick time. */ @@ -74,8 +76,16 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) cycles_elapsed = ~cycles_elapsed; /* off by one cycle - don't care */ } - ticks_elapsed += cycles_elapsed / clocktick; - cycles_remainder = cycles_elapsed % clocktick; + if (likely(cycles_elapsed < local_ct)) { + /* ticks_elapsed = 1 -- We already assumed one tick elapsed. */ + cycles_remainder = cycles_elapsed; + } 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); + } /* Can we differentiate between "early CR16" (aka Scenario 1) and * "long delay" (aka Scenario 3)? I don't think so. @@ -86,14 +96,12 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) */ if (ticks_elapsed > HZ) { /* Scenario 3: very long delay? bad in any case */ - printk (KERN_CRIT "timer_interrupt(CPU %d): delayed! run ntpdate" + printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!" " 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 */ } @@ -101,12 +109,19 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) * 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); + next_tick = now + (local_ct - cycles_remainder); + + /* 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; /* 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; + mtctl(next_tick, 16); /* Now that we are done mucking with unreliable delivery of interrupts, * go do system house keeping. @@ -169,35 +184,37 @@ gettimeoffset (void) unsigned long next_tick; unsigned long elapsed_cycles; unsigned long usec; + unsigned long cpuid = smp_processor_id(); + unsigned long local_ct = clocktick; - next_tick = cpu_data[smp_processor_id()].it_value; + next_tick = cpu_data[cpuid].it_value; now = mfctl(16); /* Read the hardware interval timer. */ - prev_tick = next_tick - clocktick; + prev_tick = next_tick - local_ct; /* 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. + * ones complement is off-by-one. Don't care. */ elapsed_cycles = ~elapsed_cycles; } - if (elapsed_cycles > (HZ * clocktick)) { + if (elapsed_cycles > (HZ * local_ct)) { /* 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); + elapsed_cycles, prev_tick, now, next_tick, local_ct); } /* 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); + usec += local_ct * (jiffies - wall_jiffies); return usec; #else return 0; @@ -290,7 +307,6 @@ void __init time_init(void) static struct pdc_tod tod_data; clocktick = (100 * PAGE0->mem_10msec) / HZ; - halftick = clocktick / 2; start_cpu_itimer(); /* get CPU 0 started */ |