linux-kernel - Re: [PATCH 5/5] kvm: optimize GFN to memslot lookup with large slots amount

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Date:	Tue, 02 Dec 2014 19:45:21 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>,
	Igor Mammedov <imammedo@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 5/5] kvm: optimize GFN to memslot lookup with large slots
 amount



On 02/12/2014 18:33, Radim Krčmář wrote:
>> > +	while (start < end) {
>> > +		slot = start + (end - start) / 2;
>> > +
>> > +		if (gfn >= memslots[slot].base_gfn)
> (Even thought division is costly, I think that checking here if 'slot'
>  is the one we want wouldn't help very much.)
> 

Division by an unsigned is just a right shift.  Division by signed
integer is a right shift + conditional move.  We can change / 2 to
explicit >> 1, or change start and end to unsigned, or both.

Paolo
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