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 4 patches reintroduce 6aa9707099c (lockdep: check that no locks held at freeze time) which was reverted in dbf520a9d7d4, and fix up the known callers with locks held in NFS and CIFS to skip the lockdep check for now. The lockdep check will warn any future incorrect users of the freezable helpers. The fifth 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 sixth patch modifies the freeze_task() function 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. v2 moves the skip check to freeze_task(), and expands the commit messages. v3 adds the patches to reintroduce the lockdep check to this patchset, adds a patch to convert the freezable helpers to static inlines when possible, and splits the patch that adds the new helpers out of the one that converts the existing helpers to use freezer_do_not_count. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
