Message-ID: <547E08C1.3090708@redhat.com>
Date: Tue, 02 Dec 2014 19:45:21 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Igor Mammedov <imammedo@redhat.com>
CC: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 5/5] kvm: optimize GFN to memslot lookup with large slots
 amount
References: <1417454967-4465-1-git-send-email-imammedo@redhat.com> <1417454967-4465-6-git-send-email-imammedo@redhat.com> <20141202173350.GA11312@potion.brq.redhat.com>
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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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