From 2fde46b79e2fdbc90d0d97cf992782732b5a371c Mon Sep 17 00:00:00 2001 From: Len Brown Date: Sun, 22 Nov 2015 18:16:15 -0500 Subject: [PATCH] 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 Signed-off-by: Len Brown Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dparsons@brightdsl.net Link: http://lkml.kernel.org/r/9082eb809ef40dad02db714759c7aaf618c518d4.1448232494.git.len.brown@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/smpboot.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) 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; } -- 2.20.1