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x86/smp/boot: Add cmdline "cpu_init_udelay=N" to specify cpu_up() delay

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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: Len 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Len Brown 2015-05-11 17:27:09 -04:00 committed by Ingo Molnar
parent 191a66353b
commit d68921f9bd
2 changed files with 28 additions and 1 deletions
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6
Documentation/kernel-parameters.txt
View file

@ -746,6 +746,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
cpuidle.off=1 [CPU_IDLE]
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
Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]

23
arch/x86/kernel/smpboot.c
View file

@ -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
* 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");
send_status = safe_apic_wait_icr_idle();
mdelay(10);
mdelay(init_udelay);
pr_debug("Deasserting INIT\n");