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x86: Reduce clock calibration time during slave cpu startup

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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>
This commit is contained in:
Jack Steiner
2011-11-15 15:33:56 -08:00
committed by Ingo Molnar
parent 1ea7c6737c
commit b565201cf7
3 changed files with 46 additions and 5 deletions
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16
arch/x86/kernel/smpboot.c
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@@ -207,22 +207,28 @@ static void __cpuinit smp_callin(void)
* Need to setup vector mappings before we enable interrupts.
*/
setup_vector_irq(smp_processor_id());
/*
* Save our processor parameters. Note: this information
* is needed for clock calibration.
*/
smp_store_cpu_info(cpuid);
/*
* Get our bogomips.
* Update loops_per_jiffy in cpu_data. Previous call to
* smp_store_cpu_info() stored a value that is close but not as
* accurate as the value just calculated.
*
* Need to enable IRQs because it can take longer and then
* the NMI watchdog might kill us.
*/
local_irq_enable();
calibrate_delay();
cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
local_irq_disable();
pr_debug("Stack at about %p\n", &cpuid);
/*
* Save our processor parameters
*/
smp_store_cpu_info(cpuid);
/*
* This must be done before setting cpu_online_mask
* or calling notify_cpu_starting.