Commit 2fde46b7 authored Nov 22, 2015 by Len Brown Committed by Ingo Molnar Nov 23, 2015

x86/smpboot: Re-enable init_udelay=0 by default on modern CPUs



Fix a Linux-4.3 corner case performance regression, introduced by commit:

  f1ccd249 ("x86/smpboot: Fix cpu_init_udelay=10000 corner case boot parameter misbehavior")

which allowed the cmdline  "cpu_init_udelay=" to work with all values,
including the default of 10000.

But in setting the default of 10000, it over-rode the code stat sets
the delay 0 on modern processors.

Also, tidy up use of INT/UINT.

Reported-by: Shane <shrybman@teksavvy.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dparsons@brightdsl.net
Link: http://lkml.kernel.org/r/9082eb809ef40dad02db714759c7aaf618c518d4.1448232494.git.len.brown@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 72613184

arch/x86/kernel/smpboot.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -509,7 +509,7 @@ void __inquire_remote_apic(int apicid)
		*/
		#define UDELAY_10MS_DEFAULT 10000

		static unsigned int init_udelay = INT_MAX;
		static unsigned int init_udelay = UINT_MAX;

		static int __init cpu_init_udelay(char *str)
		{
		@@ -522,14 +522,15 @@ 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 != INT_MAX)
		if (init_udelay != UINT_MAX)
		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)))
		((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86 >= 0xF))) {
		init_udelay = 0;

		return;
		}
		/* else, use legacy delay */
		init_udelay = UDELAY_10MS_DEFAULT;
		}