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

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Message-ID: <20150917143527.GJ3604@twins.programming.kicks-ass.net>
Date:	Thu, 17 Sep 2015 16:35:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Paul Turner <pjt@...gle.com>, 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

On Sat, Sep 12, 2015 at 10:40:07AM -0400, Tejun Heo wrote:
> So, one of the problems is that the kernel can't have tasks w/o
> runnable CPUs, so we have to some workaround when, for whatever
> reason, a task ends up with no CPU that it can run on.

No, just refuse that configuration.

> You say cpuset isn't a layering thing but that simply isn't true.
> It's a cgroup-scope CPU mask.  It layers atop task affinities
> restricting what they can be configured to, limiting the effective
> cpumask to the intersection of actually existing CPUs and overriding
> individual affinity setting when the intersection doesn't exist.

No, just fail.

> The kernel does not update all CPU affinity masks when a CPU goes down
> or comes up.

I'd be happy to fail a CPU down for user tasks where this is the last
runnable CPU of.
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