Disable interrupts while testing the timer. Not doing this unnecessarily

added an arbitrary delay to our readings, causing us to use the ACPI-safe
read method when not necessary.  Submitted by: bde

Old:
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks BAD  min = 3, max = 19, width = 16
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks BAD  min = 3, max = 19, width = 16
ACPI timer looks GOOD min = 3, max = 5, width = 2
ACPI timer looks GOOD min = 3, max = 4, width = 1
Timecounter "ACPI-safe" frequency 3579545 Hz quality 1000

New:
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
ACPI timer looks GOOD min = 3, max = 4, width = 1
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000

Also, reduce unnecesary overhead in ACPI-fast by remove the barrier for
reads.  The timer in the ACPI-fast case is known to increase monotonically
so there is no need to serialize access to it.

1 files changed, 7 insertions, 6 deletions

diff --git a/sys/dev/acpica/acpi_timer.c b/sys/dev/acpica/acpi_timer.c
index 69342a1..2de7810 100644
--- a/sys/dev/acpica/acpi_timer.c
+++ b/sys/dev/acpica/acpi_timer.c
@@ -99,12 +99,7 @@ static struct timecounter acpi_timer_timecounter = {
 static u_int
 acpi_timer_read()
 {
-    uint32_t tv;
-
-    tv = bus_space_read_4(acpi_timer_bst, acpi_timer_bsh, 0);
-    bus_space_barrier(acpi_timer_bst, acpi_timer_bsh, 0, 4,
-	BUS_SPACE_BARRIER_READ);
-    return (tv);
+    return (bus_space_read_4(acpi_timer_bst, acpi_timer_bsh, 0));
 }
 
 /*
@@ -277,9 +272,13 @@ acpi_timer_test()
 {
     uint32_t	last, this;
     int		min, max, n, delta;
+    register_t	s;
 
     min = 10000000;
     max = 0;
+
+    /* Test the timer with interrupts disabled to get accurate results. */
+    s = intr_disable();
     last = acpi_timer_read();
     for (n = 0; n < N; n++) {
 	this = acpi_timer_read();
@@ -290,6 +289,8 @@ acpi_timer_test()
 	    min = delta;
 	last = this;
     }
+    intr_restore(s);
+
     if (max - min > 2)
 	n = 0;
     else if (min < 0 || max == 0)