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Commit d68921f9 authored by Len Brown's avatar Len Brown Committed by Ingo Molnar
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x86/smp/boot: Add cmdline "cpu_init_udelay=N" to specify cpu_up() delay 



No change to default behavior.

Replace the hard-coded mdelay(10) in cpu_up() with a variable
udelay, that is set to a defined default -- rather than a magic
number.

Add a boot-time override, "cpu_init_udelay=N"

Signed-off-by: default avatarLen Brown <len.brown@intel.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jan H. Schönherr <jschoenh@amazon.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2fe8e6c798e8def271122f62df9bbf58dc283e2a.1431379433.git.len.brown@intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 191a6635

Documentation/kernel-parameters.txt

+6 −0
Original line number Original line Diff line number Diff line
@@ -746,6 +746,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
	cpuidle.off=1	[CPU_IDLE]

	cpuidle.off=1	[CPU_IDLE]

			disable the cpuidle sub-system

			disable the cpuidle sub-system





	cpu_init_udelay=N

			[X86] Delay for N microsec between assert and de-assert

			of APIC INIT to start processors.  This delay occurs

			on every CPU online, such as boot, and resume from suspend.

			Default: 10000



	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver

	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver

			Format:

			Format:

			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]

			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]

arch/x86/kernel/smpboot.c

+22 −1
Original line number Original line Diff line number Diff line
@@ -513,6 +513,27 @@ void __inquire_remote_apic(int apicid) 
	}

	}

}

}





/*

 * The Multiprocessor Specification 1.4 (1997) example code suggests

 * that there should be a 10ms delay between the BSP asserting INIT

 * and de-asserting INIT, when starting a remote processor.

 * But that slows boot and resume on modern processors, which include

 * many cores and don't require that delay.

 *

 * Cmdline "init_cpu_udelay=" is available to over-ride this delay.

 */

#define UDELAY_10MS_DEFAULT 10000



static unsigned int init_udelay = UDELAY_10MS_DEFAULT;



static int __init cpu_init_udelay(char *str)

{

	get_option(&str, &init_udelay);



	return 0;

}

early_param("cpu_init_udelay", cpu_init_udelay);



/*

/*

 * Poke the other CPU in the eye via NMI to wake it up. Remember that the normal

 * Poke the other CPU in the eye via NMI to wake it up. Remember that the normal

 * INIT, INIT, STARTUP sequence will reset the chip hard for us, and this

 * INIT, INIT, STARTUP sequence will reset the chip hard for us, and this
@@ -584,7 +605,7 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip) 
		pr_debug("Waiting for send to finish...\n");

		pr_debug("Waiting for send to finish...\n");

		send_status = safe_apic_wait_icr_idle();

		send_status = safe_apic_wait_icr_idle();





		mdelay(10);

		mdelay(init_udelay);





		pr_debug("Deasserting INIT\n");

		pr_debug("Deasserting INIT\n");