From: Len Brown <len.brown@intel.com>
Date: Sun, 22 Nov 2015 23:16:15 +0000 (-0500)
Subject: x86/smpboot: Re-enable init_udelay=0 by default on modern CPUs
X-Git-Tag: v4.5-rc1~168^2~9
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=2fde46b79e2fdbc90d0d97cf992782732b5a371c;p=karo-tx-linux.git

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

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

  f1ccd249319e ("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>
---

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 892ee2e5ecbc..fbabe4fcc7fb 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -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;
 }