On Thu, Jan 24, 2019 at 12:30:09PM +0000, Patrick Bellasi wrote:

On 23-Jan 21:11, Peter Zijlstra wrote:

quoted

Anyway, once you get range composition defined; that should be something
like:

	R_p \Compose_g R_g

Where R_p is the range of task-p, and R_g is the range of the g'th
cgroup of p (where you can make an identity between the root cgroup and
the system default).

Now; as per the other email; I think the straight forward composition:

struct range compose(struct range a, struct range b)
{
	return (range){.min = clamp(a.min, b.min, b.max),
	               .max = clamp(a.max, b.min, b.max), };
}

This composition is done in uclamp_effective_get() but it's
slightly different, since we want to support a "nice policy" where
tasks can always ask less then what they have got assigned.

Not sure I follow..

Thus, from an abstract standpoint, if a task is in a cgroup:

     task.min <= R_g.min
     task.max <= R_g.max

While, for tasks in the root cgroup system default applies and we
enforece:

     task.min >= R_0.min
     task.max <= R_0.max

... where the "nice policy" is currently not more supported, but
perhaps we can/should use the same for system defaults too.

That seems inconsistent at best.

OK, I'll go have another look. I never recognised that function for
doing that.