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Date: Mon, 24 Aug 2015 17:02:23 -0400
From: Tejun Heo <tj@kernel.org>
To: Paul Turner <pjt@google.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 3/3] sched: Implement interface for cgroup unified
 hierarchy
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Hello,

On Mon, Aug 24, 2015 at 01:54:08PM -0700, Paul Turner wrote:
> > That alone doesn't require hierarchical resource distribution tho.
> > Setting nice levels reasonably is likely to alleviate most of the
> > problem.
> 
> Nice is not sufficient here.  There could be arbitrarily many threads
> within the hypervisor that are not actually hosting guest CPU threads.
> The only way to have this competition occur at a reasonably fixed
> ratio is a sub-hierarchy.

I get that having hierarchy of threads would be nicer but am having a
bit of difficulty seeing why adjusting priorities of threads wouldn't
be sufficient.  It's not like threads of the same process competing
with each other is a new problem.  People have been dealing with it
for ages.  Hierarchical management can be a nice plus but we want the
problem and proposed solution to be justifiable.

Thanks.

-- 
tejun