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

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Date:	Tue, 2 Feb 2016 02:57:40 +0000
From:	"Zengtao (B)" <prime.zeng@...ilicon.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Monday, February 01, 2016 4:43 PM
> To: Zengtao (B)
> Cc: Arnd Bergmann; LKML; Frederic Weisbecker
> 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.

Yes, agree, a lot of places it has been used as 32bit value. Beyond that, I think 
it is more reasonable to use 64bit. 

> 
> Thanks,
> 
> 	tglx
>