diff options
author | Venki Pallipadi <venkatesh.pallipadi@intel.com> | 2008-11-17 16:11:37 -0800 |
---|---|---|
committer | Ingo Molnar <mingo@elte.hu> | 2008-12-16 21:02:50 +0100 |
commit | 40fb17152c50a69dc304dd632131c2f41281ce44 (patch) | |
tree | ae4ab9fc72183968d4e3ff5c5d07cf7573954455 /arch/x86/kernel/cpu/amd.c | |
parent | 7e91a122b11bb250d08ab125afd2c232c87502e1 (diff) | |
download | op-kernel-dev-40fb17152c50a69dc304dd632131c2f41281ce44.zip op-kernel-dev-40fb17152c50a69dc304dd632131c2f41281ce44.tar.gz |
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 <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/kernel/cpu/amd.c')
-rw-r--r-- | arch/x86/kernel/cpu/amd.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 8f1e31d..7c878f6 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); |