diff options
author | Jack Steiner <steiner@sgi.com> | 2011-11-16 03:33:56 +0400 |
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committer | Ingo Molnar <mingo@elte.hu> | 2011-12-05 20:12:43 +0400 |
commit | b565201cf75210614903ef2ae5917b4379681647 (patch) | |
tree | 6d28d33cf25a4fa47700b12d8e291886e1af195f /arch/x86/kernel/tsc.c | |
parent | 1ea7c6737c8f68453f55c894b3d07d7f48fcbef8 (diff) | |
download | linux-b565201cf75210614903ef2ae5917b4379681647.tar.xz |
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 <steiner@sgi.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: John Stultz <john.stultz@linaro.org>
[fix CONFIG_SMP=n build]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/kernel/tsc.c')
-rw-r--r-- | arch/x86/kernel/tsc.c | 20 |
1 files changed, 20 insertions, 0 deletions
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 |