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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
