diff options
| author | Len Brown | 2014-12-16 01:52:07 -0500 |
|---|---|---|
| committer | Rafael J. Wysocki | 2014-12-17 02:26:28 +0100 |
| commit | b73026b9c959600bcd65eeae7a5f7ac00ded886f (patch) | |
| tree | a95a286bd8bde9f152624390921f76ec049bb516 /drivers/cpuidle | |
| parent | 4108b3d96273784f697dd6d8e59ef9203a10a02d (diff) | |
cpuidle: ladder: Better idle duration measurement without using CPUIDLE_FLAG_TIME_INVALID
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@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpuidle')
| -rw-r--r-- | drivers/cpuidle/governors/ladder.c | 7 |
1 files changed, 1 insertions, 6 deletions
diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c index 37263d9a1051..401c0106ed34 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 && |