From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161576AbcHEPl5 (ORCPT ); Fri, 5 Aug 2016 11:41:57 -0400 Received: from mail-wm0-f53.google.com ([74.125.82.53]:36802 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161551AbcHEPlw (ORCPT ); Fri, 5 Aug 2016 11:41:52 -0400 From: Leo Yan To: Ingo Molnar , Peter Zijlstra , Vincent Guittot , linux-kernel@vger.kernel.org Cc: Leo Yan Subject: [PATCH v2] sched/fair: refine maximum periods for decay_load Date: Fri, 5 Aug 2016 23:40:59 +0800 Message-Id: <1470411659-28584-1-git-send-email-leo.yan@linaro.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In current code, decay_load() will consider to set load value to zero after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0. Kernel can support maximum number of processes and threads to 2^29 and set task with highest priority with nice=-20 (weight = 88761). So in worst case, one CPU may have maximum load value is: max_load = 2^29 * 88761 < 2^46 In theory after pass 46 periods we can ensure load value to be decayed to zero. So this patch is to change maximum periods from 64 to 46. Signed-off-by: Leo Yan --- kernel/sched/fair.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e342159..bbd01eb 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2622,7 +2622,15 @@ static __always_inline u64 decay_load(u64 val, u64 n) if (!n) return val; - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) + /* + * Kernel can support maximum number of processes and threads up to + * 2^29 and task has highest weight 88761 with nice=-20. + * + * maximum load = 2^29 * 88761 < 2^46 + * + * So pass 46 periods can ensure maximum load to be decayed to zero. + */ + else if (unlikely(n >= LOAD_AVG_PERIOD * 46)) return 0; /* after bounds checking we can collapse to 32-bit */ -- 1.9.1