Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755249Ab0DIGVW (ORCPT ); Fri, 9 Apr 2010 02:21:22 -0400 Received: from ozlabs.org ([203.10.76.45]:46431 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750806Ab0DIGVU (ORCPT ); Fri, 9 Apr 2010 02:21:20 -0400 To: Peter Zijlstra , Benjamin Herrenschmidt From: Michael Neuling Date: Fri, 09 Apr 2010 16:21:18 +1000 Subject: [PATCH 1/5] sched: fix capacity calculations for SMT4 In-Reply-To: <1270794078.794237.347827867455.qpush@pale> CC: , , Ingo Molnar , Suresh Siddha , Gautham R Shenoy Message-Id: <20100409062118.D4096CBB6C@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1970 Lines: 63 When calculating capacity we use the following calculation: capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE); In SMT2, power will be 1178/2 (provided we are not scaling power with freq say) and SCHED_LOAD_SCALE will be 1024, resulting in capacity being 1. With SMT4 however, power will be 1178/4, hence capacity will end up as 0. Fix this by ensuring capacity is always at least 1 after this calculation. Signed-off-by: Michael Neuling --- I'm not sure this is the correct fix but this works for me. Original post here: http://lkml.org/lkml/2010/3/30/884 --- kernel/sched_fair.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) Index: linux-2.6-ozlabs/kernel/sched_fair.c =================================================================== --- linux-2.6-ozlabs.orig/kernel/sched_fair.c +++ linux-2.6-ozlabs/kernel/sched_fair.c @@ -1482,6 +1482,7 @@ static int select_task_rq_fair(struct ta } capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE); + capacity = max(capacity, 1UL); if (tmp->flags & SD_POWERSAVINGS_BALANCE) nr_running /= 2; @@ -2488,6 +2489,7 @@ static inline void update_sg_lb_stats(st sgs->group_capacity = DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE); + sgs->group_capacity = max(sgs->group_capacity, 1UL); } /** @@ -2795,9 +2797,11 @@ find_busiest_queue(struct sched_group *g for_each_cpu(i, sched_group_cpus(group)) { unsigned long power = power_of(i); - unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE); + unsigned long capacity; unsigned long wl; + capacity = max(DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE), 1UL); + if (!cpumask_test_cpu(i, cpus)) continue; -- 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/