From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763671AbYD1FqY (ORCPT ); Mon, 28 Apr 2008 01:46:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753153AbYD1Fpy (ORCPT ); Mon, 28 Apr 2008 01:45:54 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:41545 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751903AbYD1Fpx (ORCPT ); Mon, 28 Apr 2008 01:45:53 -0400 Subject: Re: [PATCH] sched: fair-group: fix a Div0 error of the fair group scheduler From: Peter Zijlstra To: miaox@cn.fujitsu.com Cc: Ingo Molnar , Linux-Kernel In-Reply-To: <481558A0.9020803@cn.fujitsu.com> References: <481558A0.9020803@cn.fujitsu.com> Content-Type: text/plain Date: Mon, 28 Apr 2008 07:45:44 +0200 Message-Id: <1209361544.6429.4.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2008-04-28 at 12:54 +0800, Miao Xie wrote: > When I echoed 0 into the "cpu.shares" file, a Div0 error occured. > > We found it is caused by the following calling. > > sched_group_set_shares(tg, shares) > set_se_shares(tg->se[i], shares/nr_cpu_ids) > __set_se_shares(se, shares) > div64_64((1ULL<<32), shares) > > When the echoed value was less than the number of processores, the result of the > sentence "shares/nr_cpu_ids" was 0, and then the system called div64() to divide > the result, the Div0 error occured. > > It is unnecessary that the shares value is divided by nr_cpu_ids, I think. > Because in the function __update_group_shares_cpu() and init_tg_cfs_entry(), > the shares value isn't divided by nr_cpu_ids when setting shares of the sched > entity. > > This patch fixes this bug. And echoing ULONG_MAX value into cpu.shares also > causes Div0 error, so we set a macro MAX_SHARES to limit the max value of > shares. how about: diff --git a/kernel/sched.c b/kernel/sched.c index 740fb40..b68127a 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -8025,7 +8025,7 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq, se->my_q = cfs_rq; se->load.weight = tg->shares; - se->load.inv_weight = div64_64(1ULL<<32, se->load.weight); + se->load.inv_weight = 0; se->parent = parent; } #endif @@ -8692,7 +8692,7 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares) dequeue_entity(cfs_rq, se, 0); se->load.weight = shares; - se->load.inv_weight = div64_64((1ULL<<32), shares); + se->load.inv_weight = 0; if (on_rq) enqueue_entity(cfs_rq, se, 0);