[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>

diff --git a/arch/parisc/kernel/time.c b/arch/parisc/kernel/time.c
index fd425e1..c43e847 100644 (file)
--- 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 */