Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 4 Jan 2002 08:37:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 4 Jan 2002 08:37:18 -0500 Received: from penguin.e-mind.com ([195.223.140.120]:13416 "EHLO penguin.e-mind.com") by vger.kernel.org with ESMTP id ; Fri, 4 Jan 2002 08:37:04 -0500 Date: Fri, 4 Jan 2002 14:36:59 +0100 From: Andrea Arcangeli To: Ingo Molnar Cc: David Lang , Dieter =?iso-8859-1?Q?N=FCtzel?= , Linux Kernel List Subject: Re: [announce] [patch] ultra-scalable O(1) SMP and UP scheduler Message-ID: <20020104143659.I1561@athlon.random> In-Reply-To:

Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.12i In-Reply-To: ; from mingo@elte.hu on Fri, Jan 04, 2002 at 12:44:57PM +0100 X-GnuPG-Key-URL: http://e-mind.com/~andrea/aa.gnupg.asc X-PGP-Key-URL: http://e-mind.com/~andrea/aa.asc Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 04, 2002 at 12:44:57PM +0100, Ingo Molnar wrote: > > On Fri, 4 Jan 2002, David Lang wrote: > > > Ingo, > > back in the 2.4.4-2.4.5 days when we experimented with the > > child-runs-first scheduling patch we ran into quite a few programs that > > died or locked up due to this. (I had a couple myself and heard of others) > > hm, Andrea said that the only serious issue was in the sysvinit code, > which should be fixed in any recent distro. Andrea? correct. I run child-run-first always on all my boxes. And those races could trigger also before, so it's better to make them more easily reproducible anyways. I always run with this patch applied: diff -urN parent-timeslice/include/linux/sched.h child-first/include/linux/sched.h --- parent-timeslice/include/linux/sched.h Thu May 3 18:17:56 2001 +++ child-first/include/linux/sched.h Thu May 3 18:19:44 2001 @@ -301,7 +301,7 @@ * all fields in a single cacheline that are needed for * the goodness() loop in schedule(). */ - int counter; + volatile int counter; int nice; unsigned int policy; struct mm_struct *mm; diff -urN parent-timeslice/kernel/fork.c child-first/kernel/fork.c --- parent-timeslice/kernel/fork.c Thu May 3 18:18:31 2001 +++ child-first/kernel/fork.c Thu May 3 18:20:40 2001 @@ -665,15 +665,18 @@ p->pdeath_signal = 0; /* - * "share" dynamic priority between parent and child, thus the - * total amount of dynamic priorities in the system doesnt change, - * more scheduling fairness. This is only important in the first - * timeslice, on the long run the scheduling behaviour is unchanged. + * Scheduling the child first is especially useful in avoiding a + * lot of copy-on-write faults if the child for a fork() just wants + * to do a few simple things and then exec(). */ - p->counter = (current->counter + 1) >> 1; - current->counter >>= 1; - if (!current->counter) + { + int counter = current->counter; + p->counter = (counter + 1) >> 1; + current->counter = counter >> 1; + p->policy &= ~SCHED_YIELD; + current->policy |= SCHED_YIELD; current->need_resched = 1; + } /* Tell the parent if it can get back its timeslice when child exits */ p->get_child_timeslice = 1; > > > try switching this back to the current behaviour and see if the > > lockups still happen. > > there must be some other bug as well, the child-runs-first scheduling can > cause lockups, but it shouldnt cause oopes. definitely. My above implementation works fine. Andrea - 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/