Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 28 Dec 2000 18:48:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 28 Dec 2000 18:48:08 -0500 Received: from Cantor.suse.de ([194.112.123.193]:37394 "HELO Cantor.suse.de") by vger.kernel.org with SMTP id ; Thu, 28 Dec 2000 18:47:57 -0500 Date: Fri, 29 Dec 2000 00:17:21 +0100 From: Andi Kleen To: "David S. Miller" Cc: ak@suse.de, torvalds@transmeta.com, marcelo@conectiva.com.br, linux-kernel@vger.kernel.org Subject: Re: test13-pre5 Message-ID: <20001229001721.B25388@gruyere.muc.suse.de> In-Reply-To:

<20001228231722.A24875@gruyere.muc.suse.de> <200012282233.OAA01433@pizda.ninka.net> <20001228235836.A25388@gruyere.muc.suse.de> <200012282254.OAA01772@pizda.ninka.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <200012282254.OAA01772@pizda.ninka.net>; from davem@redhat.com on Thu, Dec 28, 2000 at 02:54:52PM -0800 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 28, 2000 at 02:54:52PM -0800, David S. Miller wrote: > Date: Thu, 28 Dec 2000 23:58:36 +0100 > From: Andi Kleen > > Why exactly a power of two ? To get rid of ->index ? > > To make things like "page - mem_map" et al. use shifts instead of > expensive multiplies... I thought that is what ->index is for ? Also gcc seems to be already quite clever at dividing through small integers, e.g. using mul and shift and sub, so it may not be even worth to reach for a real power-of-two. I suspect doing the arithmetics is at least faster than eating the cache misses because of ->index. -Andikkk - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/