Hello, Frederic. On Wed, Aug 24, 2011 at 03:14:30AM +0200, Frederic Weisbecker wrote: > > 0001-cgroup-subsys-attach_task-should-be-called-after-mig.patch > > 0002-cgroup-improve-old-cgroup-handling-in-cgroup_attach_.patch > > 0003-cgroup-introduce-cgroup_taskset-and-use-it-in-subsys.patch > > 0004-cgroup-don-t-use-subsys-can_attach_task-or-attach_ta.patch > > 0005-cgroup-cpuset-don-t-use-ss-pre_attach.patch > > 0006-cgroup-kill-subsys-can_attach_task-pre_attach-and-at.patch > > I don't understand the point on patches 3,4,5,6 > > Why pushing the task iterations down to the subsystems? I'll try again. It seems like methods were added to serve the immediate need of the particular user at the time and that in turn led to addition of callbacks which were both superflous and incomplete (the bullet points in the original message list them). This seems to have happened because extra interface was added without trying to make the existing interface complete. The interface is complicated and cumbersome to use - are [can_]attach() called first or [can_]attach_task()? What about cancelation? What if a subsys wants to perform operations across multiple tasks atomically? In general, iteration-by-callback is painful to use. Establishing common context (be it synchronization domain or shared variables) becomes very cumbersome and implementation becomes fragmented and difficult to follow. For example, imagine how it would be like to use list if we had call_for_each_list_entry(func, list_head) instead of the control-loop style iterators we have know. So, using iterators enables making all relevant information to each stage of attach so that only one callback is required for each step - the way it should be. In addition, it makes it far easier for subsystems to implement more involved logic in their methods. I tried to make cgroup_freezer behave better which requires better synchronization against the freezer and, with the current interface, it's extremely ugly and painful. The new interface is complete, easy to understand and use with far less subtleties. Thanks. -- tejun _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
