Local APIC timer interrupt happens HZ times per second on each CPU.
Optimize it for the case where profile multiplier equals one and does
not change (99+% of cases); this saves about 20 CPU cycles on Pentium II.
Also update the old multiplier immediately after noticing it changed,
while values are register-hot, saving eight bytes of stack depth.
Signed-off-by: Chuck Ebbert <[email protected]>
diff -up 2.6.15a.orig/arch/i386/kernel/apic.c 2.6.15a/arch/i386/kernel/apic.c
--- 2.6.15a.orig/arch/i386/kernel/apic.c
+++ 2.6.15a/arch/i386/kernel/apic.c
@@ -1137,7 +1137,7 @@ inline void smp_local_timer_interrupt(st
int cpu = smp_processor_id();
profile_tick(CPU_PROFILING, regs);
- if (--per_cpu(prof_counter, cpu) <= 0) {
+ if (likely(--per_cpu(prof_counter, cpu)) <= 0) {
/*
* The multiplier may have changed since the last time we got
* to this point as a result of the user writing to
@@ -1147,13 +1147,13 @@ inline void smp_local_timer_interrupt(st
* Interrupts are already masked off at this point.
*/
per_cpu(prof_counter, cpu) = per_cpu(prof_multiplier, cpu);
- if (per_cpu(prof_counter, cpu) !=
- per_cpu(prof_old_multiplier, cpu)) {
+ if (unlikely(per_cpu(prof_counter, cpu) !=
+ per_cpu(prof_old_multiplier, cpu))) {
+ per_cpu(prof_old_multiplier, cpu) =
+ per_cpu(prof_counter, cpu);
__setup_APIC_LVTT(
calibration_result/
per_cpu(prof_counter, cpu));
- per_cpu(prof_old_multiplier, cpu) =
- per_cpu(prof_counter, cpu);
}
#ifdef CONFIG_SMP
--
Chuck
-
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