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Date: Mon, 17 Nov 2008 16:11:37 -0800
From: Venki Pallipadi <venkatesh.pallipadi@...el.com>
To: H Peter Anvin <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86: Support always running TSC on Intel CPUs
Add support for CPUID_0x80000007_Bit8 on Intel CPUs as well. This bit means
that the TSC is invariant with C/P/T states and always runs at constant
frequency.
With Intel CPUs, we have 3 classes
* CPUs where TSC runs at constant rate and does not stop n C-states
* CPUs where TSC runs at constant rate, but will stop in deep C-states
* CPUs where TSC rate will vary based on P/T-states and TSC will stop in deep
C-states.
To cover these 3, one feature bit (CONSTANT_TSC) is not enough. So, add a
second bit (NOSTOP_TSC). CONSTANT_TSC indicates that the TSC runs at
constant frequency irrespective of P/T-states, and NOSTOP_TSC indicates
that TSC does not stop in deep C-states.
CPUID_0x8000000_Bit8 indicates both these feature bit can be set.
We still have CONSTANT_TSC _set_ and NOSTOP_TSC _not_set_ on some older Intel
CPUs, based on model checks. We can use TSC on such CPUs for time, as long as
those CPUs do not support/enter deep C-states.
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
---
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/kernel/cpu/amd.c | 9 +++++++--
arch/x86/kernel/cpu/intel.c | 10 ++++++++++
arch/x86/kernel/process.c | 2 +-
drivers/acpi/processor_idle.c | 6 +++---
5 files changed, 22 insertions(+), 6 deletions(-)
Index: tip/arch/x86/kernel/cpu/amd.c
===================================================================
--- tip.orig/arch/x86/kernel/cpu/amd.c 2008-11-17 12:48:08.000000000 -0800
+++ tip/arch/x86/kernel/cpu/amd.c 2008-11-17 15:49:39.000000000 -0800
@@ -283,9 +283,14 @@ static void __cpuinit early_init_amd(str
{
early_init_amd_mc(c);
- /* c->x86_power is 8000_0007 edx. Bit 8 is constant TSC */
- if (c->x86_power & (1<<8))
+ /*
+ * c->x86_power is 8000_0007 edx. Bit 8 is TSC runs at constant rate
+ * with P/T states and does not stop in deep C-states
+ */
+ if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
+ set_cpu_cap(c, X86_FEATURE_NOSTOP_TSC);
+ }
#ifdef CONFIG_X86_64
set_cpu_cap(c, X86_FEATURE_SYSCALL32);
Index: tip/arch/x86/kernel/cpu/intel.c
===================================================================
--- tip.orig/arch/x86/kernel/cpu/intel.c 2008-11-17 12:48:08.000000000 -0800
+++ tip/arch/x86/kernel/cpu/intel.c 2008-11-17 15:49:39.000000000 -0800
@@ -41,6 +41,16 @@ static void __cpuinit early_init_intel(s
if (c->x86 == 15 && c->x86_cache_alignment == 64)
c->x86_cache_alignment = 128;
#endif
+
+ /*
+ * c->x86_power is 8000_0007 edx. Bit 8 is TSC runs at constant rate
+ * with P/T states and does not stop in deep C-states
+ */
+ if (c->x86_power & (1 << 8)) {
+ set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
+ set_cpu_cap(c, X86_FEATURE_NOSTOP_TSC);
+ }
+
}
#ifdef CONFIG_X86_32
Index: tip/drivers/acpi/processor_idle.c
===================================================================
--- tip.orig/drivers/acpi/processor_idle.c 2008-11-17 12:48:11.000000000 -0800
+++ tip/drivers/acpi/processor_idle.c 2008-11-17 15:49:39.000000000 -0800
@@ -374,15 +374,15 @@ static int tsc_halts_in_c(int state)
{
switch (boot_cpu_data.x86_vendor) {
case X86_VENDOR_AMD:
+ case X86_VENDOR_INTEL:
/*
* AMD Fam10h TSC will tick in all
* C/P/S0/S1 states when this bit is set.
*/
- if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+ if (boot_cpu_has(X86_FEATURE_NOSTOP_TSC))
return 0;
+
/*FALL THROUGH*/
- case X86_VENDOR_INTEL:
- /* Several cases known where TSC halts in C2 too */
default:
return state > ACPI_STATE_C1;
}
Index: tip/arch/x86/include/asm/cpufeature.h
===================================================================
--- tip.orig/arch/x86/include/asm/cpufeature.h 2008-11-17 12:48:08.000000000 -0800
+++ tip/arch/x86/include/asm/cpufeature.h 2008-11-17 15:50:27.000000000 -0800
@@ -93,6 +93,7 @@
#define X86_FEATURE_AMDC1E (3*32+21) /* AMD C1E detected */
#define X86_FEATURE_XTOPOLOGY (3*32+22) /* cpu topology enum extensions */
#define X86_FEATURE_TSC_RELIABLE (3*32+23) /* TSC is known to be reliable */
+#define X86_FEATURE_NOSTOP_TSC (3*32+24) /* TSC does not stop in C states */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* "pni" SSE-3 */
Index: tip/arch/x86/kernel/process.c
===================================================================
--- tip.orig/arch/x86/kernel/process.c 2008-11-17 12:48:08.000000000 -0800
+++ tip/arch/x86/kernel/process.c 2008-11-17 15:49:39.000000000 -0800
@@ -286,7 +286,7 @@ static void c1e_idle(void)
rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
if (lo & K8_INTP_C1E_ACTIVE_MASK) {
c1e_detected = 1;
- if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+ if (!boot_cpu_has(X86_FEATURE_NOSTOP_TSC))
mark_tsc_unstable("TSC halt in AMD C1E");
printk(KERN_INFO "System has AMD C1E enabled\n");
set_cpu_cap(&boot_cpu_data, X86_FEATURE_AMDC1E);
--
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