On 12/16/2014 07:52 AM, Len Brown wrote:
From: Len Brown <len.brown@xxxxxxxxx>
When the ladder governor sees the CPUIDLE_FLAG_TIME_INVALID flag,
it unconditionally causes a state promotion by setting last_residency
to a number higher than the state's promotion_time:
last_residency = last_state->threshold.promotion_time + 1
It does this for fear that cpuidle_get_last_residency()
will be in-accurate, because cpuidle_enter_state() invoked
a state with CPUIDLE_FLAG_TIME_INVALID.
But the only state with CPUIDLE_FLAG_TIME_INVALID is
acpi_safe_halt(), which may return well after its actual
idle duration because it enables interrupts, so cpuidle_enter_state()
also measures interrupt service time.
So what? In ladder, a huge invalid last_residency has exactly
the same effect as the current code -- it unconditionally
causes a state promotion.
In the case where the idle residency plus measured interrupt
handling time is less than the state's demotion_time -- we should
use that timestamp to give ladder a chance to demote, rather than
unconditionally promoting.
This can be done by simply ignoring the CPUIDLE_FLAG_TIME_INVALID,
and using the "invalid" time, as it is either equal to what we are
doing today, or better.
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Acked-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
a dumb question: is someone still using the ladder governor nowadays ?
---
drivers/cpuidle/governors/ladder.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
index 37263d9..401c010 100644
--- a/drivers/cpuidle/governors/ladder.c
+++ b/drivers/cpuidle/governors/ladder.c
@@ -79,12 +79,7 @@ static int ladder_select_state(struct cpuidle_driver *drv,
last_state = &ldev->states[last_idx];
- if (!(drv->states[last_idx].flags & CPUIDLE_FLAG_TIME_INVALID)) {
- last_residency = cpuidle_get_last_residency(dev) - \
- drv->states[last_idx].exit_latency;
- }
- else
- last_residency = last_state->threshold.promotion_time + 1;
+ last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
/* consider promotion */
if (last_idx < drv->state_count - 1 &&
--
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