While we indeed can't precisely measure time spent in C1, we can consider

measured interval as upper bound. It should be more precise then just
assuming hz/2. For idle CPU it should be quite precise, for busy - not
worse then before.

1 files changed, 7 insertions, 3 deletions

diff --git a/sys/dev/acpica/acpi_cpu.c b/sys/dev/acpica/acpi_cpu.c
index 043f0c071a20..9398fc2c8950 100644
--- a/sys/dev/acpica/acpi_cpu.c
+++ b/sys/dev/acpica/acpi_cpu.c
@@ -928,12 +928,16 @@ acpi_cpu_idle()
 
     /*
      * Execute HLT (or equivalent) and wait for an interrupt.  We can't
-     * calculate the time spent in C1 since the place we wake up is an
-     * ISR.  Assume we slept half of quantum and return.
+     * precisely calculate the time spent in C1 since the place we wake up
+     * is an ISR.  Assume we slept no more then half of quantum.
      */
     if (cx_next->type == ACPI_STATE_C1) {
-	sc->cpu_prev_sleep = (sc->cpu_prev_sleep * 3 + 500000 / hz) / 4;
+	AcpiHwRead(&start_time, &AcpiGbl_FADT.XPmTimerBlock);
 	acpi_cpu_c1();
+	AcpiHwRead(&end_time, &AcpiGbl_FADT.XPmTimerBlock);
+        end_time = acpi_TimerDelta(end_time, start_time);
+	sc->cpu_prev_sleep = (sc->cpu_prev_sleep * 3 +
+	    min(PM_USEC(end_time), 500000)) / 4;
 	return;
     }