[RFC][PATCH 2/2] ACPI: handle timer ticks proactively

[Adam Belay <abelay@novell.com>]

Hi All,

This patch takes advantage of the infrastructure introduced in the last
patch, and allows the processor idle algorithm to proactively choose a
c-state based on the time the next timer interrupt is expected to occur.
It preserves the residency metric, so the algorithm should, in theory,
remain effective against bursts of activity from other interrupt
sources.

This patch is mostly intended to be illustrative.  There may be some
"#ifdef CONFIG_ACPI" issues, and I would appreciate any advice on
implementing this more cleanly.

Cheers,
Adam

Patch is against 2.6.18-rc4.
Signed-off-by: Adam Belay <abelay@novell.com>

---
 drivers/acpi/processor_idle.c |   17 +++++++++++++++++
 include/acpi/processor.h      |    2 ++
 kernel/timer.c                |    7 +++++++
 3 files changed, 26 insertions(+)


--- a/drivers/acpi/processor_idle.c	2006-08-28 17:14:54.000000000 -0400
+++ b/drivers/acpi/processor_idle.c	2006-08-28 17:29:21.000000000 -0400
@@ -64,6 +64,7 @@
  * Currently, we aim for the entry/exit latency to be 20% of measured residency.
  */
 #define RESIDENCY_TO_LATENCY_RATIO	5
+#define TIMER_TICKS (PM_TIMER_FREQUENCY / HZ)
 
 /* --------------------------------------------------------------------------
                                 Power Management
@@ -271,6 +272,22 @@
 		int count = min(pr->power.count, (int) max_cstate);
 		cx = &pr->power.states[state_idx];
 
+		/*
+		 * We are proactive with timer interrupts.  After a timer
+		 * interrupt has occurred the previous sleep_ticks value is
+		 * restored.
+		 */
+		if (pr->power.pretimer_last_ticks) {
+			sleep_ticks = pr->power.pretimer_last_ticks;
+			pr->power.pretimer_last_ticks = 0;
+		}
+		t1 = inl(acpi_fadt.xpm_tmr_blk.address);
+		i = TIMER_TICKS - t1 + pr->power.timer_tick;
+		if (i < sleep_ticks) {
+			pr->power.pretimer_last_ticks = sleep_ticks;
+			sleep_ticks = i;
+		}
+
 		if (cx->target_ticks < sleep_ticks) { /* promotion */
 			for (i = state_idx + 1; i <= count; i++) {
 				cx = &pr->power.states[i];
--- a/kernel/timer.c	2006-08-03 13:39:22.000000000 -0400
+++ b/kernel/timer.c	2006-08-28 17:16:36.000000000 -0400
@@ -41,6 +41,9 @@
 #include <asm/timex.h>
 #include <asm/io.h>
 
+#include <acpi/acpi_bus.h>
+#include <acpi/processor.h>
+
 #ifdef CONFIG_TIME_INTERPOLATION
 static void time_interpolator_update(long delta_nsec);
 #else
@@ -1175,6 +1178,10 @@
 {
 	struct task_struct *p = current;
 	int cpu = smp_processor_id();
+	struct acpi_processor *pr = processors[cpu];
+
+	if (pr)
+		pr->power.timer_tick = inl(acpi_fadt.xpm_tmr_blk.address);
 
 	/* Note: this timer irq context must be accounted for as well. */
 	if (user_tick)
--- a/include/acpi/processor.h	2006-08-28 17:14:54.000000000 -0400
+++ b/include/acpi/processor.h	2006-08-28 17:20:25.000000000 -0400
@@ -60,6 +60,8 @@
 	u32 bm_activity;
 	u32 bm_veto_state;
 	u32 last_ticks;
+	u32 timer_tick;
+	u32 pretimer_last_ticks;
 	int count;
 	struct acpi_processor_cx states[ACPI_PROCESSOR_MAX_POWER];
 };