On Wed, Aug 24, 2011 at 09:49:59AM +0200, Tejun Heo wrote: > 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. Yeah it's true that the order between [can]attach/[can]attach_task plus the added mess with pre_attach was not entirely sane. The fact we have foo and foo_task is already a problem. I guess we indeed need to sacrifice the iteration from the cgroup core for that. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
