Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751380AbVI3BqE (ORCPT ); Thu, 29 Sep 2005 21:46:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751415AbVI3BqE (ORCPT ); Thu, 29 Sep 2005 21:46:04 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:39813 "EHLO e3.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1751380AbVI3BqD (ORCPT ); Thu, 29 Sep 2005 21:46:03 -0400 Date: Thu, 29 Sep 2005 18:46:36 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: George Anzinger , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Steven Rostedt , Jeff Dike Subject: Re: 2.6.13-rc6-rt9 Message-ID: <20050930014636.GV8177@us.ibm.com> Reply-To: paulmck@us.ibm.com References: <20050818060126.GA13152@elte.hu> <1124470574.17311.4.camel@twins> <1124476205.17311.8.camel@twins> <20050819184334.GG1298@us.ibm.com> <1124566045.17311.11.camel@twins> <20050820212446.GA9822@ccure.user-mode-linux.org> <1127980463.14695.6.camel@twins> <20050930010041.GS8177@us.ibm.com> <1128042449.15115.375.camel@tglx.tec.linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1128042449.15115.375.camel@tglx.tec.linutronix.de> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1522 Lines: 41 On Fri, Sep 30, 2005 at 03:07:29AM +0200, Thomas Gleixner wrote: > On Thu, 2005-09-29 at 18:00 -0700, Paul E. McKenney wrote: > > > Even with a current -rt (2.6.14-rc2-rt5) UML does not run. The issue is > > > indeed (as jeff pointed out) that VTALRM is never send. The small test > > > programm below illustrates this. > > > > > > On a non-rt kernel it completed in 1 second. > > > On a -rt kernel it waits at infinitum. > > > > Will play with it and see what I broke... > > Paul, > > you are not the culprit :) Woo-hoo!!! Exonerated!!! This time, anyway... ;-) > The run_posix_cpu_timers(p) call is #ifdef'd out with PREEMPT_RT. > > Thats a hard to fix issue. > > It can not be run from hardirq context, as it takes a lot of locks > (especially our favorites: tasklist_lock and sighand->siglock). :( > > Maybe another playground for rcu, but it might also be solved by some > other mechanism for accounting and delayed execution in the PREEMPT_RT > case. Certainly check_thread_timers() and check_process_timers() are playing with a number of task_struct fields, so it is not immediately clear to me how to safely replace tasklist_lock with RCU, at least not with a simple and small patch. What did you have in mind for delayed execution? Thanx, Paul - 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/