From 40fb17152c50a69dc304dd632131c2f41281ce44 Mon Sep 17 00:00:00 2001 From: Venki Pallipadi Date: Mon, 17 Nov 2008 16:11:37 -0800 Subject: x86: support always running TSC on Intel CPUs Impact: reward non-stop TSCs with good TSC-based clocksources, etc. 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 (NONSTOP_TSC). CONSTANT_TSC indicates that the TSC runs at constant frequency irrespective of P/T-states, and NONSTOP_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 NONSTOP_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 Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/amd.c | 9 +++++++-- arch/x86/kernel/cpu/intel.c | 10 ++++++++++ 2 files changed, 17 insertions(+), 2 deletions(-) (limited to 'arch/x86/kernel/cpu') diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 8f1e31db2ad..7c878f6aa91 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -283,9 +283,14 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c) { 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_NONSTOP_TSC); + } #ifdef CONFIG_X86_64 set_cpu_cap(c, X86_FEATURE_SYSCALL32); diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index cce0b6118d5..caec59437a2 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -41,6 +41,16 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c) 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_NONSTOP_TSC); + } + } #ifdef CONFIG_X86_32 -- cgit v1.2.3