linux-kernel - Re: [PATCH 1/2] KVM: Remove unnecessary divide operations

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Date:	Thu, 01 Jul 2010 17:18:13 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: Remove unnecessary divide operations

On 07/01/2010 05:00 PM, Joerg Roedel wrote:
> This patch converts unnecessary divide and modulo operations
> in the KVM large page related code into logical operations.
> This allows to convert gfn_t to u64 while not breaking 32
> bit builds.
>
>
>   #define KVM_NR_PAGE_SIZES 2
> -#define KVM_HPAGE_SHIFT(x) (PAGE_SHIFT + ((x) - 1) * 8)
> +#define KVM_HPAGE_GFN_SHIFT(x) (((x) - 1) * 8)
> +#define KVM_HPAGE_SHIFT(x) (PAGE_SHIFT + KVM_HPAGE_GFN_SHIFT(x))
>   #define KVM_HPAGE_SIZE(x) (1UL<<  KVM_HPAGE_SHIFT(x))
>   #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
>    

In theory, KVM_HPAGE_SIZE() needs s/1UL/(u64)1/, or KVM_HPAGE_MASK 
becomes truncated if used against a gfn_t.  In practice, KVM_HPAGE_MASK 
is not used at all, so this doesn't matter.

-- 
error compiling committee.c: too many arguments to function

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