cpuidle: Fix incorrect optimization

commit 672917dcc78 ("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>

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 1aea715..f8e57c6 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -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
                /*