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authorGrant Grundler <grundler@gsyprf11.external.hp.com>2006-09-04 13:56:11 -0700
committerMatthew Wilcox <willy@parisc-linux.org>2006-10-04 06:48:38 -0600
commit6b799d9222fef265802b0b6dcc4fb982cc8f55ca (patch)
treef6d276b49949f2bbf7de1213d5424eb13edf458e
parentbed583f76e1d5fbb5a6fdf27a0f7b2ae235f7e99 (diff)
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[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>
-rw-r--r--arch/parisc/kernel/time.c46
1 files changed, 31 insertions, 15 deletions
diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index fd425e1..c43e847 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 */