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cpuidle: Fix incorrect optimization 

commit 672917dcc7 ("cpuidle: menu governor: reduce latency on exit")
added an optimization, where the analysis on the past idle period moved
from the end of idle, to the beginning of the new idle.

Unfortunately, this optimization had a bug where it zeroed one key
variable for new use, that is needed for the analysis.  The fix is
simple, zero the variable after doing the work from the previous idle.

During the audit of the code that found this issue, another issue was
also found; the ->measured_us data structure member is never set, a
local variable is always used instead.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Corrado Zoccolo <czoccolo@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Arjan van de Ven 2010-05-08 15:47:37 -07:00 committed by Linus Torvalds
parent f1c448e0a9
commit 1c6fe0364f
1 changed files with 4 additions and 5 deletions
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9
drivers/cpuidle/governors/menu.c
View File

@ -100,7 +100,6 @@ struct menu_device {
int needs_update;
unsigned int expected_us;
unsigned int measured_us;
u64 predicted_us;
unsigned int exit_us;
unsigned int bucket;
@ -187,14 +186,14 @@ static int menu_select(struct cpuidle_device *dev)
int i;
int multiplier;
data->last_state_idx = 0;
data->exit_us = 0;
if (data->needs_update) {
menu_update(dev);
data->needs_update = 0;
}
data->last_state_idx = 0;
data->exit_us = 0;
/* Special case when user has set very strict latency requirement */
if (unlikely(latency_req == 0))
return 0;
@ -294,7 +293,7 @@ static void menu_update(struct cpuidle_device *dev)
new_factor = data->correction_factor[data->bucket]
* (DECAY - 1) / DECAY;
if (data->expected_us > 0 && data->measured_us < MAX_INTERESTING)
if (data->expected_us > 0 && measured_us < MAX_INTERESTING)
new_factor += RESOLUTION * measured_us / data->expected_us;
else
/*