On Thu, Feb 02, 2017 at 04:52:29PM -0500, Tejun Heo wrote:

quoted

Why do you need to manually turn it on?  That is, couldn't it be
automatic based on what controllers are enabled?

This came up already but it's not like some controllers are inherently
thread-only.  Consider CPU, all in-context CPU cycle consumptions are
tied to the thread; however, we also want to be able to account for
CPU cycles consumed for, for example, memory reclaim or encryption
during writeback.

I played with an interface where thread mode is enabled automatically
upto the common ancestor of the threads but not only was it
complicated to implement but also the eventual behavior was very
confusing as the resource domain can change without any active actions
from the user.  I think keeping things simple is the right choice
here.

Note that the explicit marking of the resource domains gets you exactly
that. But let me reply in the other subthread.