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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20141202210300.GA13037@potion.redhat.com>
Date:	Tue, 2 Dec 2014 22:03:01 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Igor Mammedov <imammedo@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH 5/5] kvm: optimize GFN to memslot lookup with large slots
 amount

2014-12-02 19:45+0100, Paolo Bonzini:
> 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.

My bad, no respectable optimizer would miss that.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/