Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759881Ab0KQIHG (ORCPT ); Wed, 17 Nov 2010 03:07:06 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:58836 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758033Ab0KQIHD (ORCPT ); Wed, 17 Nov 2010 03:07:03 -0500 Date: Wed, 17 Nov 2010 13:36:55 +0530 From: Balbir Singh To: Linus Torvalds Cc: Vivek Goyal , Mike Galbraith , Oleg Nesterov , Peter Zijlstra , Markus Trippelsdorf , Mathieu Desnoyers , Ingo Molnar , LKML Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups Message-ID: <20101117080653.GB16969@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <1289783580.495.58.camel@maggy.simson.net> <1289811438.2109.474.camel@laptop> <1289820766.16406.45.camel@maggy.simson.net> <1289821590.16406.47.camel@maggy.simson.net> <20101115125716.GA22422@redhat.com> <1289856350.14719.135.camel@maggy.simson.net> <20101116015648.GA11534@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1845 Lines: 44 * Linus Torvalds [2010-11-15 18:18:20]: > On Mon, Nov 15, 2010 at 5:56 PM, Vivek Goyal 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/