Messages in this thread | | | From | Colin Cross <> | Subject | [PATCH 00/10] optimize freezing tasks by reducing task wakeups | Date | Mon, 29 Apr 2013 14:45:36 -0700 |
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On slow cpus the large number of task wakeups and context switches triggered by freezing and thawing tasks can take a significant amount of cpu time. This patch series reduces the amount of work done during freezing tasks by avoiding waking up tasks that are already in a freezable state.
The first patch reduces the wasted time in try_to_freeze_tasks() by starting with a 1 ms sleep during the first loop and backing off up to an 8 ms sleep if all tasks are not frozen.
The second patch modifies the try_to_freeze_tasks() loop to skip tasks that have set the PF_FREEZER_SKIP flag by calling freezer_do_not_count(). These tasks will not enter the refrigerator during the suspend/resume cycle unless they woken up by something else, in which case they will enter the refrigerator in freezer_count() before they access any resources that would not be available in suspend or deadlock with another freezing/frozen task.
The rest of the series adds a few more freezable helpers and converts the top call sites that userspace tasks are usually blocked at to freezable helpers. The list of call sites was collected on a Nexus 10 (ARM Exynos 5250 SoC), but all the top call sites other than binder show up at the top of the list on Ubuntu x86-64 as well.
This series cuts the time for freezing tasks from 50 ms to 5 ms when the cpu speed is locked at its lowest setting (200MHz), and reduces the number of context switches and restarted syscalls from 1000 to 25.
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