From b73026b9c959600bcd65eeae7a5f7ac00ded886f Mon Sep 17 00:00:00 2001 From: Len Brown Date: Tue, 16 Dec 2014 01:52:07 -0500 Subject: 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 Acked-by: Daniel Lezcano Signed-off-by: Rafael J. Wysocki 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 && -- cgit v0.10.2