linux-kernel - Re: [PATCH v2 03/12] sched/fair: Change the variable to hold the number of periods to 32bit integer

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Message-ID: <20160503084742.GH3430@twins.programming.kicks-ass.net>
Date:	Tue, 3 May 2016 10:47:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...nel.org, linux-kernel@...r.kernel.org, bsegall@...gle.com,
	pjt@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, dietmar.eggemann@....com,
	juri.lelli@....com
Subject: Re: [PATCH v2 03/12] sched/fair: Change the variable to hold the
 number of periods to 32bit integer

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?