From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752799AbaEOFE3 (ORCPT ); Thu, 15 May 2014 01:04:29 -0400 Received: from mail-ee0-f49.google.com ([74.125.83.49]:39557 "EHLO mail-ee0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751421AbaEOFE0 (ORCPT ); Thu, 15 May 2014 01:04:26 -0400 Message-ID: <1400130262.5175.93.camel@marge.simpson.net> Subject: Re: [RFC 09/16] kgr: mark task_safe in some kthreads From: Mike Galbraith To: Tejun Heo Cc: Vojtech Pavlik , Jiri Slaby , Jiri Kosina , linux-kernel@vger.kernel.org, jirislaby@gmail.com, Michael Matz , Steven Rostedt , Frederic Weisbecker , Ingo Molnar , Greg Kroah-Hartman , "Theodore Ts'o" , Dipankar Sarma , "Paul E. McKenney" Date: Thu, 15 May 2014 07:04:22 +0200 In-Reply-To: <20140515045011.GB3825@htj.dyndns.org> References: <20140501142414.GA31611@htj.dyndns.org> <20140501210242.GA28948@mtj.dyndns.org> <20140501210943.GB28948@mtj.dyndns.org> <537384B9.5090907@suse.cz> <20140514151501.GA24142@suse.cz> <20140514163238.GA15690@htj.dyndns.org> <1400126037.5175.55.camel@marge.simpson.net> <20140515040608.GA3825@htj.dyndns.org> <1400129178.5175.82.camel@marge.simpson.net> <20140515045011.GB3825@htj.dyndns.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-05-15 at 00:50 -0400, Tejun Heo wrote: > Hello, Mike. > > On Thu, May 15, 2014 at 06:46:18AM +0200, Mike Galbraith wrote: > > > I think it'd be healthier to identify the use cases and then provide > > > proper interface for it. Note that workqueue can now expose interface > > > to modify concurrency, priority and cpumask to userland which > > > writeback workers are already using. > > > > You can't identify a specific thing, any/all of it can land on the > > user's diner plate, so he should be able to make the decisions. Power > > to the user and all that, if he does something stupid, tuff titty. User > > getting to call the shots, and getting to keep the pieces when he fscks > > it all up is wonderful stuff, lets kernel people off the hook :) > > Do we know specific kthreads which need to be exposed with this way? Soft/hard irq threads and anything having to do with IO mostly, which including workqueues. I had to give the user a rather fugly global prioritization option to let users more or less safely do the evil deeds they want to and WILL do whether I agree with their motivation to do so or not. I tell all users that realtime is real dangerous, but if they want to do that, it's their box, so by definition perfectly fine. > If there are good enough reasons for specific ones, sure, but I don't > think "we can't change any of the kthreads because someone might be > diddling with it" is something we can sustain in the long term. I think the opposite. Taking any control the user has is pure evil. -Mike