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Subject[PATCH 1/4] [x86] Add command line option to enable/disable hyper-threading.
Date
This patch adds a config option to allow disabling hyper-threading by
default, and a kernel command line option to changes this default at
boot time.

Signed-off-by: Ben Collins <bcollins@ubuntu.com>
---
Documentation/kernel-parameters.txt | 3 +++
arch/i386/Kconfig | 5 +++++
arch/i386/kernel/cpu/common.c | 29 +++++++++++++++++++++++++++++
3 files changed, 37 insertions(+), 0 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6747384..2b68d6e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -600,6 +600,9 @@ and is between 256 and 4096 characters.
hisax= [HW,ISDN]
See Documentation/isdn/README.HiSax.

+ ht= [HW,IA-32,SMP] Enable or disable hyper-threading.
+ Format: <on|off>
+
hugepages= [HW,IA-32,IA-64] Maximal number of HugeTLB pages.

noirqbalance [IA-32,SMP,KNL] Disable kernel irq balancing
diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 8ff1c6f..b4a2461 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -1185,6 +1185,11 @@ config X86_HT
depends on SMP && !(X86_VISWS || X86_VOYAGER)
default y

+config X86_HT_DISABLE
+ bool "Disable Hyper-Threading by default"
+ depends on X86_HT
+ default n
+
config X86_BIOS_REBOOT
bool
depends on !(X86_VISWS || X86_VOYAGER)
diff --git a/arch/i386/kernel/cpu/common.c b/arch/i386/kernel/cpu/common.c
index d9f3e3c..42d2361 100644
--- a/arch/i386/kernel/cpu/common.c
+++ b/arch/i386/kernel/cpu/common.c
@@ -482,6 +482,29 @@ void __cpuinit identify_cpu(struct cpuin
}

#ifdef CONFIG_X86_HT
+
+#ifdef CONFIG_X86_HT_DISABLE
+static int disable_ht __cpuinitdata = 1;
+#else
+static int disable_ht __cpuinitdata;
+#endif
+
+static int __init parse_ht(char *arg)
+{
+ if (!arg)
+ return -EINVAL;
+
+ if (!memcmp(arg, "on", 2))
+ disable_ht = 0;
+ else if (!memcmp(arg, "off", 3))
+ disable_ht = 1;
+ else
+ return -EINVAL;
+
+ return 0;
+}
+early_param("ht", parse_ht);
+
void __cpuinit detect_ht(struct cpuinfo_x86 *c)
{
u32 eax, ebx, ecx, edx;
@@ -492,6 +515,12 @@ void __cpuinit detect_ht(struct cpuinfo_
if (!cpu_has(c, X86_FEATURE_HT) || cpu_has(c, X86_FEATURE_CMP_LEGACY))
return;

+ if (disable_ht) {
+ printk(KERN_INFO "CPU: Hyper-Threading disabled by default. Enable with ht=on\n");
+ smp_num_siblings = 1;
+ return;
+ }
+
smp_num_siblings = (ebx & 0xff0000) >> 16;

if (smp_num_siblings == 1) {
--
1.4.1
-
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