From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754246Ab0HZWXm (ORCPT ); Thu, 26 Aug 2010 18:23:42 -0400 Received: from www.tglx.de ([62.245.132.106]:52753 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752432Ab0HZWXk (ORCPT ); Thu, 26 Aug 2010 18:23:40 -0400 Date: Fri, 27 Aug 2010 00:22:46 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: Mathieu Desnoyers , LKML , Linus Torvalds , Andrew Morton , Ingo Molnar , Steven Rostedt , Tony Lindgren , Mike Galbraith Subject: Re: [RFC PATCH 00/11] sched: CFS low-latency features In-Reply-To: Message-ID: References: <20100826180908.648103531@efficios.com> <1282849045.1975.1587.camel@laptop> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ? Thanks, tglx