Re: [PATCHSET RFC cgroup/for-4.6] cgroup, sched: implement resource group and PRIO_RGRP

[Peter Zijlstra]

On Thu, Apr 07, 2016 at 03:35:47AM -0400, Johannes Weiner wrote:
> There was a lot of back and forth whether we should add a second set
> of knobs just to control the local tasks separately from the subtree,
> but ended up concluding that the situation can be expressed more
> clearly by creating dedicated leaf subgroups for stuff like management
> software and launchers instead, so that their memory pools/LRUs are
> clearly delineated from other groups and seperately controllable. And
> we couldn't think of any meaningful configuration that could not be
> expressed in that scheme. I mean, it's the same thing, right?


No, not the same.


	R
      / | \
     t1	t2 A
         /   \
        t3   t4


Is fundamentally different from:


             R
	   /   \
	 L       A
       /   \   /   \
      t1  t2  t3   t4


Because if in the first hierarchy you add a task (t5) to R, all of its A
will run at 1/4th of total bandwidth where before it had 1/3rd, whereas
with the second example, if you add our t5 to L, A doesn't get any less
bandwidth.


Please pull your collective heads out of the systemd arse and start
thinking.