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[PARISC] remove halftick and copy clocktick to local var (gcc can optimize usage)

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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 2006-09-04 13:56:11 -07:00 committed by Matthew Wilcox
parent bed583f76e
commit 6b799d9222
1 changed files with 31 additions and 15 deletions
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46
arch/parisc/kernel/time.c
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@ -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 */