diff options
Diffstat (limited to 'arch/parisc')
| -rw-r--r-- | arch/parisc/kernel/time.c | 140 |
1 files changed, 96 insertions, 44 deletions
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c index 47831c2cd09..fd425e1abe6 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 @@ 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; + + /* 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; + } - /* the precision of this math could be improved */ - return elapsed_cycles / (PAGE0->mem_10msec / 10000); + 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; } |