From owner-freebsd-arch Sat Mar 17 10:33:16 2001 Delivered-To: freebsd-arch@freebsd.org Received: from flood.ping.uio.no (flood.ping.uio.no [129.240.78.31]) by hub.freebsd.org (Postfix) with ESMTP id 17DFD37B718 for ; Sat, 17 Mar 2001 10:33:13 -0800 (PST) (envelope-from des@ofug.org) Received: (from des@localhost) by flood.ping.uio.no (8.9.3/8.9.3) id TAA74242; Sat, 17 Mar 2001 19:33:11 +0100 (CET) (envelope-from des@ofug.org) X-URL: http://www.ofug.org/~des/ X-Disclaimer: The views expressed in this message do not necessarily coincide with those of any organisation or company with which I am or have been affiliated. To: Maxime Henrion Cc: arch@FreeBSD.org Subject: Re: Proposal for a new syscall References: <20010317164411.A420@nebula.cybercable.fr> <20010317173444.B420@nebula.cybercable.fr> <20010317183137.C420@nebula.cybercable.fr> From: Dag-Erling Smorgrav Date: 17 Mar 2001 19:33:10 +0100 In-Reply-To: Maxime Henrion's message of "Sat, 17 Mar 2001 18:31:38 +0100" Message-ID: Lines: 22 User-Agent: Gnus/5.0802 (Gnus v5.8.2) Emacs/20.4 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Maxime Henrion writes: > > > > > such a syscall in the kernel would allow to implement "zero-copy" > > > > > wherever it is feasible. > > > > No. It would save you two copies and a bunch of syscalls, but it > > > > wouldn't be real zero-copy, just "n-2 copy" instead of "n copy". > > > And if n == 2 ? > > It's never the case. I think the best you can do in userland is n = 3, > I'm talking about a syscall. Yes. I already told you that your proposed syscall would at best reduce the number of copies by two. Now I'm telling you that the minimum number of copies, without your proposed syscall, can't be less than 3. You do the math. > Why couldn't it be zero-copy if sendfile() already does this ? Sendfile(2) doesn't do zero-copy, it does 2-copy (in the best of cases). DES -- Dag-Erling Smorgrav - des@ofug.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message