Date:2009-09-22 02:04:09 (13 years 5 days ago)
Author:Corrado Zoccolo
Commit:672917dcc781ead7652a8b11b1fba14e38ac15b8
Message:cpuidle: menu governor: reduce latency on exit

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>
Files: drivers/cpuidle/governors/menu.c (5 diffs)

Change Details

drivers/cpuidle/governors/menu.c
9696
9797struct menu_device {
9898    int last_state_idx;
99    int needs_update;
99100
100101    unsigned int expected_us;
101102    u64 predicted_us;
...... 
166167
167168static DEFINE_PER_CPU(struct menu_device, menu_devices);
168169
170static void menu_update(struct cpuidle_device *dev);
171
169172/**
170173 * menu_select - selects the next idle state to enter
171174 * @dev: the CPU
...... 
180183    data->last_state_idx = 0;
181184    data->exit_us = 0;
182185
186    if (data->needs_update) {
187        menu_update(dev);
188        data->needs_update = 0;
189    }
190
183191    /* Special case when user has set very strict latency requirement */
184192    if (unlikely(latency_req == 0))
185193        return 0;
...... 
231239}
232240
233241/**
234 * menu_reflect - attempts to guess what happened after entry
242 * menu_reflect - records that data structures need update
235243 * @dev: the CPU
236244 *
237245 * NOTE: it's important to be fast here because this operation will add to
...... 
240248static void menu_reflect(struct cpuidle_device *dev)
241249{
242250    struct menu_device *data = &__get_cpu_var(menu_devices);
251    data->needs_update = 1;
252}
253
254/**
255 * menu_update - attempts to guess what happened after entry
256 * @dev: the CPU
257 */
258static void menu_update(struct cpuidle_device *dev)
259{
260    struct menu_device *data = &__get_cpu_var(menu_devices);
243261    int last_idx = data->last_state_idx;
244262    unsigned int last_idle_us = cpuidle_get_last_residency(dev);
245263    struct cpuidle_state *target = &dev->states[last_idx];

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