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Diffstat (limited to 'Documentation/power/freezing-of-tasks.txt')
| -rw-r--r-- | Documentation/power/freezing-of-tasks.txt | 29 |
1 files changed, 25 insertions, 4 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index 6ccb68f68da..ec715cd78fb 100644 --- a/Documentation/power/freezing-of-tasks.txt +++ b/Documentation/power/freezing-of-tasks.txt @@ -63,6 +63,27 @@ devices have been reinitialized, the function thaw_processes() is called in order to clear the PF_FROZEN flag for each frozen task. Then, the tasks that have been frozen leave __refrigerator() and continue running. + +Rationale behind the functions dealing with freezing and thawing of tasks: +------------------------------------------------------------------------- + +freeze_processes(): + - freezes only userspace tasks + +freeze_kernel_threads(): + - freezes all tasks (including kernel threads) because we can't freeze + kernel threads without freezing userspace tasks + +thaw_kernel_threads(): + - thaws only kernel threads; this is particularly useful if we need to do + anything special in between thawing of kernel threads and thawing of + userspace tasks, or if we want to postpone the thawing of userspace tasks + +thaw_processes(): + - thaws all tasks (including kernel threads) because we can't thaw userspace + tasks without thawing kernel threads + + III. Which kernel threads are freezable? Kernel threads are not freezable by default. However, a kernel thread may clear @@ -120,10 +141,10 @@ So in practice, the 'at all' may become a 'why freeze kernel threads?' and freezing user threads I don't find really objectionable." Still, there are kernel threads that may want to be freezable. For example, if -a kernel that belongs to a device driver accesses the device directly, it in -principle needs to know when the device is suspended, so that it doesn't try to -access it at that time. However, if the kernel thread is freezable, it will be -frozen before the driver's .suspend() callback is executed and it will be +a kernel thread that belongs to a device driver accesses the device directly, it +in principle needs to know when the device is suspended, so that it doesn't try +to access it at that time. However, if the kernel thread is freezable, it will +be frozen before the driver's .suspend() callback is executed and it will be thawed after the driver's .resume() callback has run, so it won't be accessing the device while it's suspended. |