linux-kernel - Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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Message-ID: <20101117080653.GB16969@balbir.in.ibm.com>
Date:	Wed, 17 Nov 2010 13:36:55 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

* Linus Torvalds <torvalds@...ux-foundation.org> [2010-11-15 18:18:20]:

> On Mon, Nov 15, 2010 at 5:56 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> >
> > Should this kind of thing be done in user space?
> 
> Almost certainly not.
>
> First off, user-space is a fragmented mess. Just from a "let's get it
> done" angle, it just doesn't work. There are lots of different thing
> that create new tty's, and you can't have them all fixed. Plus it
> would be _way_ more code in user space than it is in kernel space.
>
> Secondly, user-space daemons are a total mess. We've tried it many
> many times, and every time the _intention_ is to make things simpler
> to debug and deploy. And it almost never is. The interfaces end up
> being too painful, and the "part of the code is in kernel space, part
> of it is in user space" means that things just break all the time.
> 

Please elaborate, is this a generic statement or a comment on
cgclassify or cgroup user rules.

> Finally, the whole "user space is more flexible" is just a lie. It
> simply doesn't end up being true. It will be _harder_ to configure
> some user-space daemon than it is to just set a flag in /sys or
> whatever. The "flexibility" tends to be more a flexibility to get
> things wrong than any actual advantage.
> 
> Just look at the patch in question. It's simple, it's clean, and it
> "just works". Doing the same thing in user space? It would be a total
> nightmare, and exactly _because_ it would be a total nightmare, the
> code would never be that simple or clean.
> 
>                        Linus

-- 
	Three Cheers,
	Balbir
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