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Message-ID: <20120202022829.13341.64259.stgit@srivatsabhat.in.ibm.com> Date: Thu, 02 Feb 2012 07:58:33 +0530 From: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com> To: rjw@...k.pl Cc: tj@...nel.org, pavel@....cz, len.brown@...el.com, rdunlap@...otime.net, linux-pm@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH] PM/Freezer/Docs: Document the beauty of freeze/thaw semantics The way the different freeze/thaw functions encapsulate each other are quite lovely from a design point of view. And as a side-effect, the way in which they are invoked (cleaning up on failure for example) differs significantly from how usual functions are dealt with. This is because of the underlying semantics that govern the freezing and thawing of various tasks. This subtle aspect that differentiates these functions from the rest, is worth documenting. Many thanks to Tejun Heo for providing enlightenment on this topic. Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com> --- Documentation/power/freezing-of-tasks.txt | 21 +++++++++++++++++++++ 1 files changed, 21 insertions(+), 0 deletions(-) diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt index ebd7490..ec715cd 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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