netdev - Re: [PATCH 2/5] accounting unit and variable

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Message-Id: <20071113.195549.181119456.davem@davemloft.net>
Date:	Tue, 13 Nov 2007 19:55:49 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	haoki@...hat.com
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	satoshi.oshima.fk@...achi.com, andi@...stfloor.org,
	shemminger@...ux-foundation.org, johnpol@....mipt.ru,
	yoshfuji@...ux-ipv6.org, yumiko.sugita.yf@...achi.com
Subject: Re: [PATCH 2/5] accounting unit and variable

From: Hideo AOKI <haoki@...hat.com>
Date: Tue, 13 Nov 2007 22:27:13 -0500

> Herbert Xu wrote:
> > On Mon, Oct 29, 2007 at 05:23:10PM -0400, Hideo AOKI wrote:
> >>  
> >> +#define SK_DATAGRAM_MEM_QUANTUM ((int)PAGE_SIZE)
> >> +
> >> +static inline int sk_datagram_pages(int amt)
> >> +{
> >> +	return DIV_ROUND_UP(amt, SK_DATAGRAM_MEM_QUANTUM);
> >> +}
> > 
> > Does this really have to be int? Unsigned would let the compiler
> > optimise this to a simple shift.
> 
> Thank you for the comment.
> 
> This inline function is used to calculate the first argument of atomic_add()
> and atomic_sub(). Since the argument is int, I believe that using int is
> better than using unsigned int.

If you know the values will always be positive, as you will know here,
it is OK to us unsigned int here and avoids the unacceptable expensive
divide instruction.

Please fix this.
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