ACPI: Don't let acpi_pad needlessly mark TSC unstable
acpi pad driver kind of aggressively marks TSC as unstable at init
time, on mwait capable and non X86_FEATURE_NONSTOP_TSC systems. This is
irrespective of whether pad driver is ever going to be used on the
system or deep C-states are supported/used. This will affect every user
who just happens to compile in (or get a kernel version which
compiles in) acpi pad driver.
Move mark_tsc_unstable() out of init to the actual idle invocation path
of the pad driver.
There is also another bug/missing_feature in the code that it does not
support 'always running apic timer' and switches to broadcast mode
unconditionally. Shaohua, can you take a look at that please.
Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c
index 6212213..f169e51 100644
--- a/drivers/acpi/acpi_pad.c
+++ b/drivers/acpi/acpi_pad.c
@@ -43,6 +43,10 @@
#define CPUID5_ECX_EXTENSIONS_SUPPORTED (0x1)
#define CPUID5_ECX_INTERRUPT_BREAK (0x2)
static unsigned long power_saving_mwait_eax;
+
+static unsigned char tsc_detected_unstable;
+static unsigned char tsc_marked_unstable;
+
static void power_saving_mwait_init(void)
{
unsigned int eax, ebx, ecx, edx;
@@ -87,8 +91,8 @@
/*FALL THROUGH*/
default:
- /* TSC could halt in idle, so notify users */
- mark_tsc_unstable("TSC halts in idle");
+ /* TSC could halt in idle */
+ tsc_detected_unstable = 1;
}
#endif
}
@@ -178,6 +182,11 @@
expire_time = jiffies + HZ * (100 - idle_pct) / 100;
while (!need_resched()) {
+ if (tsc_detected_unstable && !tsc_marked_unstable) {
+ /* TSC could halt in idle, so notify users */
+ mark_tsc_unstable("TSC halts in idle");
+ tsc_marked_unstable = 1;
+ }
local_irq_disable();
cpu = smp_processor_id();
clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER,