From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759535AbcHEIRW (ORCPT ); Fri, 5 Aug 2016 04:17:22 -0400 Received: from mail-pf0-f179.google.com ([209.85.192.179]:34300 "EHLO mail-pf0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752947AbcHEIRM (ORCPT ); Fri, 5 Aug 2016 04:17:12 -0400 Date: Fri, 5 Aug 2016 16:17:02 +0800 From: Leo Yan To: Vincent Guittot Cc: Ingo Molnar , Peter Zijlstra , linux-kernel Subject: Re: [PATCH] sched/fair: refine maximum periods for decay_load Message-ID: <20160805081702.GA21369@leoy-linaro> References: <1470378840-15206-1-git-send-email-leo.yan@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vincent, Thanks for review. On Fri, Aug 05, 2016 at 09:56:46AM +0200, Vincent Guittot wrote: > Hi Leo, > > On 5 August 2016 at 08:34, Leo Yan wrote: > > > > 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 will be decayed > > to zero. So this patch is to change maximum periods from 64 to 48. > > > > Signed-off-by: Leo Yan > > --- > > kernel/sched/fair.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index e342159..55cb134 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n) > > > > if (!n) > > return val; > > - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) > > + else if (unlikely(n > LOAD_AVG_PERIOD * 47)) > > In the equation above, you use 46 then you mentioned : "change maximum > periods from 64 to 48." and finally you use 47. Sorry introduce confusion. I want to align to 16 so choose maximum periods to 48, and due to condition is (n > LOAD_AVG_PERIOD * 47) so it equeals to (n >= LOAD_AVG_PERIOD * 48). Precisely I think the code should be: else if (unlikely(n >= LOAD_AVG_PERIOD * 46)) Do you think this is okay? > > return 0; > > > > /* after bounds checking we can collapse to 32-bit */ > > -- > > 1.9.1 > >