[PATCH] [18/20] x86: Don't disable TSC in any C states on AMD Fam10h

Andi Kleen
2008-01-03T00:55:58Z

The ACPI code currently disables TSC use in any C2 and C3
states. But the AMD Fam10h BKDG documents that the TSC
will never stop in any C states when the CONSTANT_TSC bit is
set. Make this disabling conditional on CONSTANT_TSC
not set on AMD.

I actually think this is true on Intel too for C2 states
on CPUs with p-state invariant TSC, but this needs
further discussions with Len to really confirm :-)

So far it is only enabled on AMD.

Cc: lenb@kernel.org

Signed-off-by: Andi Kleen <ak@suse.de>

---
drivers/acpi/processor_idle.c | 32 ++++++++++++++++++++++++++++----
1 file changed, 28 insertions(+), 4 deletions(-)

Index: linux/drivers/acpi/processor_idle.c
===================================================================
--- linux.orig/drivers/acpi/processor_idle.c
+++ linux/drivers/acpi/processor_idle.c
@@ -353,6 +353,26 @@ int acpi_processor_resume(struct acpi_de
return 0;
}

+#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
+static int tsc_halts_in_c(int state)
+{
+ switch (boot_cpu_data.x86_vendor) {
+ case X86_VENDOR_AMD:
+ /*
+ * 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))
+ return 0;
+ /*FALL THROUGH*/
+ case X86_VENDOR_INTEL:
+ /* Several cases known where TSC halts in C2 too */
+ default:
+ return state > ACPI_STATE_C1;
+ }
+}
+#endif
+
#ifndef CONFIG_CPU_IDLE
static void acpi_processor_idle(void)
{
@@ -512,7 +532,8 @@ static void acpi_processor_idle(void)

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
/* TSC halts in C2, so notify users */
- mark_tsc_unstable("possible TSC halt in C2");
+ if (tsc_halts_in_c(ACPI_STATE_C2))
+ mark_tsc_unstable("possible TSC halt in C2");
#endif
/* Compute time (ticks) that we were actually asleep */
sleep_ticks = ticks_elapsed(t1, t2);
@@ -576,7 +597,8 @@ static void acpi_processor_idle(void)

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
/* TSC halts in C3, so notify users */
- mark_tsc_unstable("TSC halts in C3");
+ if (tsc_halts_in_c(ACPI_STATE_C3))
+ mark_tsc_unstable("TSC halts in C3");
#endif
/* Compute time (ticks) that we were actually asleep */
sleep_ticks = ticks_elapsed(t1, t2);
@@ -1441,7 +1463,8 @@ static int acpi_idle_enter_simple(struct

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
/* TSC could halt in idle, so notify users */
- mark_tsc_unstable("TSC halts in idle");;
+ if (tsc_halts_in_c(cx->type))
+ mark_tsc_unstable("TSC halts in idle");;
#endif
sleep_ticks = ticks_elapsed(t1, t2);

@@ -1552,7 +1575,8 @@ static int acpi_idle_enter_bm(struct cpu

#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
/* TSC could halt in idle, so notify users */
- mark_tsc_unstable("TSC halts in idle");
+ if (tsc_halts_in_c(ACPI_STATE_C3))
+ mark_tsc_unstable("TSC halts in idle");
#endif
sleep_ticks = ticks_elapsed(t1, t2);
/* Tell the scheduler how much we idled: */