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 --- drivers/acpi/processor_idle.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'drivers/acpi') diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index 5f8d746a9b81..38aca048e951 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; } -- cgit v1.2.1