linux-kernel - RE: [PATCH] cputime: Fix timeval-->cputime conversion

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Date:	Mon, 1 Feb 2016 09:43:14 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Zengtao (B)" <prime.zeng@...ilicon.com>
cc:	Arnd Bergmann <arnd@...db.de>, LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: RE: [PATCH] cputime: Fix timeval-->cputime conversion

On Mon, 1 Feb 2016, Zengtao (B) wrote:

> Hi Arnd:
> 	I have got a new idea about the problem: 
> In include/linux/time64.h
> #define NSEC_PER_SEC	1000000000L 
> I think we should change it to
> #define NSEC_PER_SEC	1000000000LL 
> 
> My reason is :
> 1.  when it is used in a multiplication, it will easily get overflow.
> 2.  when it don't get overflow, the change has no side affect.

That's not a good idea. NSEC_PER_SEC is used in lots of places with 32bit
storage. I really don't want to mop up all the fallout.

Thanks,

	tglx