From b565201cf75210614903ef2ae5917b4379681647 Mon Sep 17 00:00:00 2001 From: Jack Steiner Date: Tue, 15 Nov 2011 15:33:56 -0800 Subject: x86: Reduce clock calibration time during slave cpu startup Reduce the startup time for slave cpus. Adds hooks for an arch-specific function for clock calibration. These hooks are used on x86. If a newly started cpu has the same phys_proc_id as a core already active, uses the TSC for the delay loop and has a CONSTANT_TSC, use the already-calculated value of loops_per_jiffy. This patch reduces the time required to start slave cpus on a 4096 cpu system from: 465 sec OLD 62 sec NEW This reduces boot time on a 4096p system by almost 7 minutes. Nice... Signed-off-by: Jack Steiner Cc: "H. Peter Anvin" Cc: John Stultz [fix CONFIG_SMP=n build] Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar --- arch/x86/kernel/tsc.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'arch/x86/kernel/tsc.c') diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index db483369f10b..490fb330be87 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -995,3 +995,23 @@ void __init tsc_init(void) check_system_tsc_reliable(); } +#ifdef CONFIG_SMP +/* + * If we have a constant TSC and are using the TSC for the delay loop, + * we can skip clock calibration if another cpu in the same socket has already + * been calibrated. This assumes that CONSTANT_TSC applies to all + * cpus in the socket - this should be a safe assumption. + */ +unsigned long __cpuinit calibrate_delay_is_known(void) +{ + int i, cpu = smp_processor_id(); + + if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC)) + return 0; + + for_each_online_cpu(i) + if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id) + return cpu_data(i).loops_per_jiffy; + return 0; +} +#endif -- cgit v1.2.3-59-g8ed1b