Re: [PATCH 2/2][V2] cpuidle - optimize the select function for the 'menu' governor
From: Francesco Lavra <hidden>
Date: 2012-12-16 16:11:46
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Hi Daniel, On 12/14/2012 02:57 PM, Daniel Lezcano wrote:
quoted hunk ↗ jump to hunk
As the power is backward sorted in the states array and we are looking for the state consuming the little power as possible, instead of looking from the beginning of the array, we look from the end. That should save us some iterations in the loop each time we select a state at idle time. Signed-off-by: Daniel Lezcano <redacted> --- drivers/cpuidle/governors/menu.c | 12 ++++++------ 1 files changed, 6 insertions(+), 6 deletions(-)diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index fe343a0..05b8998 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c@@ -367,24 +367,24 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) * Find the idle state with the lowest power while satisfying * our constraints. */ - for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) { + for (i = drv->state_count - 1; i >= CPUIDLE_DRIVER_STATE_START; i--) { struct cpuidle_state *s = &drv->states[i]; struct cpuidle_state_usage *su = &dev->states_usage[i]; if (s->disabled || su->disable) continue; - if (s->target_residency > data->predicted_us) { - low_predicted = 1; - continue; - } if (s->exit_latency > latency_req) continue; + if (s->target_residency > data->predicted_us) + continue; if (s->exit_latency * multiplier > data->predicted_us) continue; + low_predicted = i - CPUIDLE_DRIVER_STATE_START;
You are altering the semantics of low_predicted, which is supposed to be non-zero when the deepest C-state has not been chosen because its target residency is more than the predicted residency. It seems to me that the if block where target_residency is compared with the predicted residency should be left as is.
data->last_state_idx = i;
data->exit_us = s->exit_latency;
- }
+ break;
+ }
/* not deepest C-state chosen for low predicted residency */
if (low_predicted) {-- Francesco