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

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Date:	Thu,  3 Jan 2008 01:50:14 +0100 (CET)
From:	Andi Kleen <ak@...e.de>
To:	lenb@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [18/20] x86: Don't disable TSC in any C states on AMD Fam10h


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@...nel.org

Signed-off-by: Andi Kleen <ak@...e.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: */
--
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