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Subject[PATCH 2/2] x86: remove 10ms delay from cpu_up() on modern processors
Date
From: Len Brown <len.brown@intel.com>

Modern processor familes do not require the 10ms delay
in cpu_up() to de-assert INIT. This speeds up boot
and resume by 10ms per (application) processor.

Signed-off-by: Len Brown <len.brown@intel.com>
---
arch/x86/kernel/smpboot.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0629a8e..85bd6aa 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -521,6 +521,7 @@ void __inquire_remote_apic(int apicid)
* many cores and don't require that delay.
*
* Cmdline "init_cpu_udelay=" is available to over-ride this delay.
+ * Modern processor families are quirked to remove the delay entirely.
*/
#define UDELAY_10MS_DEFAULT 10000

@@ -534,6 +535,18 @@ static int __init cpu_init_udelay(char *str)
}
early_param("cpu_init_udelay", cpu_init_udelay);

+static void __init smp_quirk_init_udelay(void)
+{
+ /* if cmdline changed it from default, leave it alone */
+ if (init_udelay != UDELAY_10MS_DEFAULT)
+ return;
+
+ /* if modern processor, use no delay */
+ if (((boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) && (boot_cpu_data.x86 == 6)) ||
+ ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86 >= 0xF)))
+ init_udelay = 0;
+}
+
/*
* 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
@@ -1210,6 +1223,8 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
uv_system_init();

set_mtrr_aps_delayed_init();
+
+ smp_quirk_init_udelay();
}

void arch_enable_nonboot_cpus_begin(void)
--
2.4.0.rc1


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