linux-kernel - Re: sched_fair: vruntime and min

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Message-Id: <20100305161458.3A8D.A69D9226@jp.fujitsu.com>
Date:	Fri,  5 Mar 2010 16:20:43 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	figo zhang <figo1802@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: sched_fair: vruntime and min_vruntime will be overflow?

> hi,
> 
> when enqueue or dequeue the task, the se->vruntime and cfs_rq->min_vruntime will
> increased, i want to know it is will be overflow in future time?

Let's quick calculation.

type of vruntime is u64.

1 year =   365 x 24 x 60 x 60 x 1000 x 1000 x 1000 nanosec
           ~= 3 x 10^16
           ~= 2^55
2^64 / 2^55 = 2^9 ~= 500 year.

then, 500 years after you can see overflow if you still live. :)

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