From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754641Ab0HZXJj (ORCPT ); Thu, 26 Aug 2010 19:09:39 -0400 Received: from mail.openrapids.net ([64.15.138.104]:58879 "EHLO blackscsi.openrapids.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753148Ab0HZXJh (ORCPT ); Thu, 26 Aug 2010 19:09:37 -0400 Date: Thu, 26 Aug 2010 19:09:34 -0400 From: Mathieu Desnoyers To: Thomas Gleixner Cc: Peter Zijlstra , LKML , Linus Torvalds , Andrew Morton , Ingo Molnar , Steven Rostedt , Tony Lindgren , Mike Galbraith Subject: Re: [RFC PATCH 00/11] sched: CFS low-latency features Message-ID: <20100826230934.GA4194@Krystal> References: <20100826180908.648103531@efficios.com> <1282849045.1975.1587.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://www.efficios.com X-Operating-System: Linux/2.6.26-2-686 (i686) X-Uptime: 19:07:01 up 216 days, 1:43, 3 users, load average: 0.00, 0.02, 0.00 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner (tglx@linutronix.de) wrote: > On Thu, 26 Aug 2010, Thomas Gleixner wrote: > > On Thu, 26 Aug 2010, Peter Zijlstra wrote: > > > > > > Fudging fork seems dubious at best, it seems generated by the use of > > > timer_create(.evp->sigev_notify = SIGEV_THREAD), which is a really > > > broken thing to do, it has very ill defined semantics and is utterly > > > unable to properly cope with error cases. Furthermore its trivial to > > > actually correctly implement the desired behaviour, so I'm really > > > skeptical on this front; friends don't let friends use SIGEV_THREAD. > > > > SIGEV_THREAD is the best proof that the whole posix timer interface > > was comitte[e]d under the influence of not to be revealed > > mind-altering substances. > > > > I completely object to add timer specific wakeup magic and support for > > braindead fork orgies to the kernel proper. All that mess can be fixed > > in user space by using sensible functionality. > > > > Providing support for misdesigned crap just for POSIX compliance > > reasons and to make some of the blind abusers of that very same crap > > happy would be a completely stupid decision. > > > > In fact that would make a brilliant precedence case for forcing the > > kernel to solve user space madness at the expense of kernel > > complexity. If we follow down that road we get requests for extra > > functionality for AIO, networking and whatever in a split second with > > no real good reason to reject them anymore. > > I really risked eye cancer and digged into the glibc code. > > /* There is not much we can do if the allocation fails. */ > (void) pthread_create (&th, &tk->attr, timer_sigev_thread, td); > > So if the helper thread which gets the signal fails to create the > thread then everything is toast. > > What about fixing the f*cked up glibc implementation in the first place > instead of fiddling in the kernel to support this utter madness? > > WTF can't the damned delivery thread not be created when timer_create > is called and the signal be delivered to that very thread directly via > SIGEV_THREAD_ID ? Yeah, that sounds exactly like what I proposed about an hour ago on IRC ;) I'm pretty sure that would work. The only thing we might have to be careful about is what happens if the timer re-fires before the thread completes its execution. We might want to let the signal handler detect these overruns somehow. Thanks, Mathieu > > Thanks, > > tglx -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com