From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754662Ab0HZXSM (ORCPT ); Thu, 26 Aug 2010 19:18:12 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:58404 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754282Ab0HZXSJ (ORCPT ); Thu, 26 Aug 2010 19:18:09 -0400 Date: Thu, 26 Aug 2010 16:18:06 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: Peter Zijlstra , 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 Message-ID: <20100826231806.GK2367@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com 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: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 27, 2010 at 12:22:46AM +0200, Thomas Gleixner 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 ? C'mon, Thomas!!! That is entirely too sensible!!! ;-) But if you are going to create the thread at timer_create() time, why not just have the new thread block for the desired duration? Thanx, Paul