linux-kernel - Re: [PATCH 3/3] sched: Implement interface for cgroup unified hierarchy

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Message-ID: <20150824211707.GJ28944@mtj.duckdns.org>
Date:	Mon, 24 Aug 2015 17:17:07 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Paul Turner <pjt@...gle.com>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>, lizefan@...wei.com,
	cgroups <cgroups@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-team <kernel-team@...com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3] sched: Implement interface for cgroup unified
 hierarchy

Hello,

On Mon, Aug 24, 2015 at 02:10:17PM -0700, Paul Turner wrote:
> Suppose that we have 10 vcpu threads and 100 support threads.
> Suppose that we want the support threads to receive up to 10% of the
> time available to the VM as a whole on that machine.
> 
> If I have one particular support thread that is busy, I want it to
> receive that entire 10% (maybe a guest is pounding on scsi for
> example, or in the thread-pool case, I've passed a single expensive
> computation).  Conversely, suppose the guest is doing lots of
> different things and several support threads are active, I want the
> time to be shared between them.
> 
> There is no way to implement this with nice.  Either a single thread
> can consume 10%, and the group can dominate, or the group cannot
> dominate and the single thread can be starved.

Would it be possible for you to give realistic and concrete examples?
I'm not trying to play down the use cases but concrete examples are
usually helpful at putting things in perspective.

Thanks.

-- 
tejun
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