From owner-freebsd-questions@FreeBSD.ORG Sun Apr 23 02:50:29 2006 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 78C6B16A403 for ; Sun, 23 Apr 2006 02:50:29 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from pi.codefab.com (pi.codefab.com [199.103.21.227]) by mx1.FreeBSD.org (Postfix) with ESMTP id 1713743D48 for ; Sun, 23 Apr 2006 02:50:29 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from localhost (localhost [127.0.0.1]) by pi.codefab.com (Postfix) with ESMTP id 5846D5D58; Sat, 22 Apr 2006 22:50:28 -0400 (EDT) X-Virus-Scanned: amavisd-new at codefab.com Received: from pi.codefab.com ([127.0.0.1]) by localhost (pi.codefab.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NmyIG5Id-EWJ; Sat, 22 Apr 2006 22:50:27 -0400 (EDT) Received: from [192.168.1.3] (pool-68-160-235-217.ny325.east.verizon.net [68.160.235.217]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by pi.codefab.com (Postfix) with ESMTP id 3B66F5C98; Sat, 22 Apr 2006 22:50:27 -0400 (EDT) Message-ID: <444AEB7E.1030406@mac.com> Date: Sat, 22 Apr 2006 22:50:38 -0400 From: Chuck Swiger User-Agent: Thunderbird 1.5.0.2 (Windows/20060308) MIME-Version: 1.0 To: Ted Mittelstaedt References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: freebsd-questions Subject: Re: anyone understand torvald's critique of freebsd? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 23 Apr 2006 02:50:29 -0000 Ted Mittelstaedt wrote: > Then why does Linus think manipulating the VM page table mappings > is bad? That is, why does he -really- think it's bad, not the > publically-given reason? Is it because Linux is extrordinairly > inefficient in page table mappings due to some structural decision > that Linus made that cannot be reversed now, that it could never > be any good at it? Or is there some other reason? I can't speak with certainty as to what someone else might think; no doubt Linus is entirely capable of explaining his own position should you wish to inquire, however.... :-) I think Linus doesn't care much for Zero-copy sockets because for the common case of 1500/1504-byte MTU, you end up wasting at least 60% of a 4096-byte page for each packet, and maybe ?three? times that much if your hardware splits the packet into separate pages for the mbuf header, the packet headers, and the packet data. I think FreeBSD doesn't enable Zero-copy sockets by default because those are legitimate criticisms, but there is some interest and potential for benefits from them, at least for some other circumstances like jumbo ethernet frames. -- -Chuck