Messages in this thread Patch in this message | | | Date | Wed, 4 Jan 2006 13:48:09 -0500 | From | Chuck Ebbert <> | Subject | [patch 2.6.15] i386: Optimize local APIC timer interrupt code |
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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 <76306.1226@compuserve.com>
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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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