diff options
| -rw-r--r-- | arch/parisc/kernel/time.c | 88 |
1 files changed, 53 insertions, 35 deletions
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c index d97d07f47a55..a79c6f9e7e2c 100644 --- a/arch/parisc/kernel/time.c +++ b/arch/parisc/kernel/time.c @@ -56,9 +56,9 @@ static unsigned long clocktick __read_mostly; /* timer cycles per tick */ */ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id) { - unsigned long now; + unsigned long now, now2; unsigned long next_tick; - unsigned long cycles_elapsed, ticks_elapsed; + unsigned long cycles_elapsed, ticks_elapsed = 1; unsigned long cycles_remainder; unsigned int cpu = smp_processor_id(); struct cpuinfo_parisc *cpuinfo = &per_cpu(cpu_data, cpu); @@ -71,44 +71,24 @@ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id) /* Initialize next_tick to the expected tick time. */ next_tick = cpuinfo->it_value; - /* Get current interval timer. - * CR16 reads as 64 bits in CPU wide mode. - * CR16 reads as 32 bits in CPU narrow mode. - */ + /* Get current cycle counter (Control Register 16). */ now = mfctl(16); cycles_elapsed = now - next_tick; - if ((cycles_elapsed >> 5) < cpt) { + if ((cycles_elapsed >> 6) < cpt) { /* use "cheap" math (add/subtract) instead * of the more expensive div/mul method */ cycles_remainder = cycles_elapsed; - ticks_elapsed = 1; while (cycles_remainder > cpt) { cycles_remainder -= cpt; ticks_elapsed++; } } else { + /* TODO: Reduce this to one fdiv op */ cycles_remainder = cycles_elapsed % cpt; - ticks_elapsed = 1 + cycles_elapsed / cpt; - } - - /* 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 (unlikely(ticks_elapsed > HZ)) { - /* Scenario 3: very long delay? bad in any case */ - printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!" - " cycles %lX rem %lX " - " next/now %lX/%lX\n", - cpu, - cycles_elapsed, cycles_remainder, - next_tick, now ); + ticks_elapsed += cycles_elapsed / cpt; } /* convert from "division remainder" to "remainder of clock tick" */ @@ -122,18 +102,56 @@ irqreturn_t __irq_entry timer_interrupt(int irq, void *dev_id) cpuinfo->it_value = next_tick; - /* Skip one clocktick on purpose if we are likely to miss next_tick. - * We want to avoid the new next_tick being less than CR16. - * If that happened, itimer wouldn't fire until CR16 wrapped. - * We'll catch the tick we missed on the tick after that. + /* Program the IT when to deliver the next interrupt. + * Only bottom 32-bits of next_tick are writable in CR16! */ - if (!(cycles_remainder >> 13)) - next_tick += cpt; - - /* Program the IT when to deliver the next interrupt. */ - /* Only bottom 32-bits of next_tick are written to cr16. */ mtctl(next_tick, 16); + /* Skip one clocktick on purpose if we missed next_tick. + * The new CR16 must be "later" than current CR16 otherwise + * itimer would not fire until CR16 wrapped - e.g 4 seconds + * later on a 1Ghz processor. We'll account for the missed + * tick on the next timer interrupt. + * + * "next_tick - now" will always give the difference regardless + * if one or the other wrapped. If "now" is "bigger" we'll end up + * with a very large unsigned number. + */ + now2 = mfctl(16); + if (next_tick - now2 > cpt) + mtctl(next_tick+cpt, 16); + +#if 1 +/* + * GGG: DEBUG code for how many cycles programming CR16 used. + */ + if (unlikely(now2 - now > 0x3000)) /* 12K cycles */ + printk (KERN_CRIT "timer_interrupt(CPU %d): SLOW! 0x%lx cycles!" + " cyc %lX rem %lX " + " next/now %lX/%lX\n", + cpu, now2 - now, cycles_elapsed, cycles_remainder, + next_tick, now ); +#endif + + /* Can we differentiate between "early CR16" (aka Scenario 1) and + * "long delay" (aka Scenario 3)? I don't think so. + * + * Timer_interrupt will 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. + * + * It's important NO printk's are between reading CR16 and + * setting up the next value. May introduce huge variance. + */ + if (unlikely(ticks_elapsed > HZ)) { + /* Scenario 3: very long delay? bad in any case */ + printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!" + " cycles %lX rem %lX " + " next/now %lX/%lX\n", + cpu, + cycles_elapsed, cycles_remainder, + next_tick, now ); + } /* Done mucking with unreliable delivery of interrupts. * Go do system house keeping. |