From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755646AbcECIr4 (ORCPT ); Tue, 3 May 2016 04:47:56 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:36492 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755401AbcECIrv (ORCPT ); Tue, 3 May 2016 04:47:51 -0400 Date: Tue, 3 May 2016 10:47:42 +0200 From: Peter Zijlstra To: Yuyang Du Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, juri.lelli@arm.com Subject: Re: [PATCH v2 03/12] sched/fair: Change the variable to hold the number of periods to 32bit integer Message-ID: <20160503084742.GH3430@twins.programming.kicks-ass.net> References: <1462226078-31904-1-git-send-email-yuyang.du@intel.com> <1462226078-31904-4-git-send-email-yuyang.du@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1462226078-31904-4-git-send-email-yuyang.du@intel.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 03, 2016 at 05:54:29AM +0800, Yuyang Du wrote: > In sched average update, a period is about 1ms, so a 32-bit unsigned > integer can approximately hold a maximum of 49 (=2^32/1000/3600/24) > days, which means it is big enough and 64-bit is needless. This fails to explain _why_ 49 days is enough. And what the 49 days is enough for. What happens when a task sleeps for more than 49 days?