[linux-pm] [patch 1/2] cpuidle: use last_state which can reflect the actual state entered
Kevin Hilman
khilman at deeprootsystems.com
Wed Oct 1 04:09:11 PDT 2008
Venkatesh Pallipadi <venkatesh.pallipadi at intel.com> writes:
> cpuidle accounts the idle time for the C-state it was trying to enter and
> not to the actual state that the driver eventually entered. The driver may
> select a different state than the one chosen by cpuidle due to
> constraints like bus-mastering, etc.
>
> Change the time acounting code to look at the dev->last_state after
> returning from target_state->enter(). Driver can modify dev->last_state
> internally, inside the enter routine to reflect the actual C-state
> entered.
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi at intel.com>
>
> ---
> drivers/cpuidle/cpuidle.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> Index: tip/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- tip.orig/drivers/cpuidle/cpuidle.c 2008-09-23 13:52:59.000000000 -0700
> +++ tip/drivers/cpuidle/cpuidle.c 2008-09-23 14:22:43.000000000 -0700
> @@ -71,8 +71,11 @@ static void cpuidle_idle_call(void)
> target_state = &dev->states[next_state];
>
> /* enter the state and update stats */
> - dev->last_residency = target_state->enter(dev, target_state);
> dev->last_state = target_state;
> + dev->last_residency = target_state->enter(dev, target_state);
> + if (dev->last_state)
> + target_state = dev->last_state;
> +
> target_state->time += (unsigned long long)dev->last_residency;
> target_state->usage++;
Under what conditions would the enter hook set dev->last_sate to NULL?
Having the check seems to indicate it's possilble.
A minor nit-pick... why not explicitly do the accounting using
'last_state' like below. While functionally the same as above, this
makes it makes it more explicit when reading the code that the
accounting is done using 'last_state' and not 'target_state.'
Kevin
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 5ce07b5..c1294f5 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -67,10 +67,10 @@ static void cpuidle_idle_call(void)
target_state = &dev->states[next_state];
/* enter the state and update stats */
- dev->last_residency = target_state->enter(dev, target_state);
dev->last_state = target_state;
- target_state->time += (unsigned long long)dev->last_residency;
- target_state->usage++;
+ dev->last_residency = target_state->enter(dev, target_state);
+ dev->last_state->time += (unsigned long long)dev->last_residency;
+ dev->last_state->usage++;
/* give the governor an opportunity to reflect on the outcome */
if (cpuidle_curr_governor->reflect)
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