linux-kernel - Re: [PATCH v8 04/14] task_isolation: add initial support

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Message-ID: <20151020202929.485a1ef0@grimm.local.home>
Date:	Tue, 20 Oct 2015 20:29:29 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Chris Metcalf <cmetcalf@...hip.com>,
	Gilad Ben Yossef <giladb@...hip.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 04/14] task_isolation: add initial support

On Tue, 20 Oct 2015 14:26:34 -0700
Andy Lutomirski <luto@...capital.net> wrote:

> I'm not a scheduler person, so I don't know.  But "don't run me unless
> I'm isolated" seems like a design that will, at best, only ever work
> by dumb luck.  You have to disable migration, avoid other runnable
> tasks, hope that the kernel keeps working the way it did when you
> wrote the patch, hope you continue to get lucky enough that you ever
> get to user mode in the first place, etc.


Since it only makes sense to run one isolated task per cpu (not more
than one on the same CPU), I wonder if we should add a new interface
for this, that would force everything else off the CPU that it
requests. That is, you bind a task to a CPU, and then change it to
SCHED_ISOLATED (or what not), and the kernel will force all other tasks
off that CPU. Well, we would still have kernel threads, but that's a
different matter.

Also, doesn't RCU need to have a few ticks go by before it can safely
disable itself from userspace? I recall something like that. Paul?

-- Steve
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