linux-kernel - Re: [PATCH] sched: Relax a restriction in sched_rt_can

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Message-ID: <1430709236.3129.42.camel@gmail.com>
Date:	Mon, 04 May 2015 05:13:56 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Zefan Li <lizefan@...wei.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH] sched: Relax a restriction in sched_rt_can_attach()

On Mon, 2015-05-04 at 08:54 +0800, Zefan Li wrote:
> It's allowed to promote a task from normal to realtime after it has been
> attached to a non-root cgroup, but it will fail if the attaching happens
> after it has become realtime. I don't see how this restriction is useful.

In the CONFIG_RT_GROUP_SCHED case, promotion will fail is there is no
bandwidth allocated.

> We are moving toward unified hierarchy where all the cgroup controllers
> are bound together, so it would make cgroups easier to use if we have less
> restrictions on attaching tasks between cgroups.

Forcing group scheduling overhead on users if they want cpuset or memory
cgroup functionality would be far from wonderful.  Am I interpreting the
implications of this unification/binding properly?

(I hope not, surely the plan is not to utterly _destroy_ cgroup utility)

	-Mike

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