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 --- init/calibrate.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'init/calibrate.c') diff --git a/init/calibrate.c b/init/calibrate.c index 24df7976816c..5f117ca9e069 100644 --- a/init/calibrate.c +++ b/init/calibrate.c @@ -246,6 +246,19 @@ recalibrate: static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 }; +/* + * Check if cpu calibration delay is already known. For example, + * some processors with multi-core sockets may have all cores + * with the same calibration delay. + * + * Architectures should override this function if a faster calibration + * method is available. + */ +unsigned long __attribute__((weak)) __cpuinit calibrate_delay_is_known(void) +{ + return 0; +} + void __cpuinit calibrate_delay(void) { unsigned long lpj; @@ -265,6 +278,8 @@ void __cpuinit calibrate_delay(void) lpj = lpj_fine; pr_info("Calibrating delay loop (skipped), " "value calculated using timer frequency.. "); + } else if ((lpj = calibrate_delay_is_known())) { + ; } else if ((lpj = calibrate_delay_direct()) != 0) { if (!printed) pr_info("Calibrating delay using timer " -- cgit v1.2.3-59-g8ed1b