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authorVenki Pallipadi <venkatesh.pallipadi@intel.com>2008-11-17 16:11:37 -0800
committerIngo Molnar <mingo@elte.hu>2008-12-16 21:02:50 +0100
commit40fb17152c50a69dc304dd632131c2f41281ce44 (patch)
treeae4ab9fc72183968d4e3ff5c5d07cf7573954455 /drivers/acpi
parent7e91a122b11bb250d08ab125afd2c232c87502e1 (diff)
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 'drivers/acpi')
-rw-r--r--drivers/acpi/processor_idle.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 5f8d746a9b8..38aca048e95 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -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_NONSTOP_TSC))
return 0;
+
/*FALL THROUGH*/
- case X86_VENDOR_INTEL:
- /* Several cases known where TSC halts in C2 too */
default:
return state > ACPI_STATE_C1;
}