From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753529Ab0CWRjJ (ORCPT ); Tue, 23 Mar 2010 13:39:09 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:43654 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753425Ab0CWRjH (ORCPT ); Tue, 23 Mar 2010 13:39:07 -0400 From: Will Deacon To: linux-kernel@vger.kernel.org Cc: Will Deacon , Catalin Marinas , Ingo Molnar , Andrew Morton , Peter Zijlstra Subject: [PATCH] sched: prevent compiler from optimising sched_avg_update loop Date: Tue, 23 Mar 2010 17:36:45 +0000 Message-Id: <1269365805-17280-1-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 1.6.3.3 X-OriginalArrivalTime: 23 Mar 2010 17:37:10.0832 (UTC) FILETIME=[779C9B00:01CACAAF] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org GCC 4.4.1 on ARM has been observed to replace the while loop in sched_avg_update with a call to uldivmod, resulting in the following build failure at link-time: kernel/built-in.o: In function `sched_avg_update': /linux-2.6/kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod' /linux-2.6/kernel/sched.c:1261: undefined reference to `__aeabi_uldivmod' make: *** [.tmp_vmlinux1] Error 1 This patch [taken against 2.6.34-rc2] replaces the loop with a call to div_s64 which allows the Kernel to link. Cc: Catalin Marinas Cc: Ingo Molnar Cc: Andrew Morton Cc: Peter Zijlstra Signed-off-by: Will Deacon --- kernel/sched.c | 7 +++---- 1 files changed, 3 insertions(+), 4 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 9ab3cd7..6b74f21 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -1238,11 +1238,10 @@ static u64 sched_avg_period(void) static void sched_avg_update(struct rq *rq) { s64 period = sched_avg_period(); + s64 elapsed_periods = div_s64(rq->clock - rq->age_stamp - 1, period); - while ((s64)(rq->clock - rq->age_stamp) > period) { - rq->age_stamp += period; - rq->rt_avg /= 2; - } + rq->age_stamp += (u64)(elapsed_periods * period); + rq->rt_avg >>= elapsed_periods; } static void sched_rt_avg_update(struct rq *rq, u64 rt_delta) -- 1.6.3.3