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cpuidle: menu governor: reduce latency on exit

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Move the state residency accounting and statistics computation off the hot
exit path.

On exit, the need to recompute statistics is recorded, and new statistics
will be computed when menu_select is called again.

The expected effect is to reduce processor wakeup latency from sleep
(C-states).  We are speaking of few hundreds of cycles reduction out of a
several microseconds latency (determined by the hardware transition), so
it is difficult to measure.

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Adam Belay <abelay@novell.com
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Corrado Zoccolo 2009-09-21 17:04:09 -07:00 committed by Linus Torvalds
parent 69d25870f2
commit 672917dcc7
1 changed files with 19 additions and 1 deletions
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20
drivers/cpuidle/governors/menu.c
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@ -96,6 +96,7 @@
struct menu_device {
int last_state_idx;
int needs_update;
unsigned int expected_us;
u64 predicted_us;
@ -166,6 +167,8 @@ static inline int performance_multiplier(void)
static DEFINE_PER_CPU(struct menu_device, menu_devices);
static void menu_update(struct cpuidle_device *dev);
/**
* menu_select - selects the next idle state to enter
* @dev: the CPU
@ -180,6 +183,11 @@ static int menu_select(struct cpuidle_device *dev)
data->last_state_idx = 0;
data->exit_us = 0;
if (data->needs_update) {
menu_update(dev);
data->needs_update = 0;
}
/* Special case when user has set very strict latency requirement */
if (unlikely(latency_req == 0))
return 0;
@ -231,13 +239,23 @@ static int menu_select(struct cpuidle_device *dev)
}
/**
* menu_reflect - attempts to guess what happened after entry
* menu_reflect - records that data structures need update
* @dev: the CPU
*
* NOTE: it's important to be fast here because this operation will add to
* the overall exit latency.
*/
static void menu_reflect(struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
data->needs_update = 1;
}
/**
* menu_update - attempts to guess what happened after entry
* @dev: the CPU
*/
static void menu_update(struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
int last_idx = data->last_state_idx;