From owner-freebsd-current Tue Jun 13 00:32:39 1995 Return-Path: current-owner Received: (from majordom@localhost) by freefall.cdrom.com (8.6.10/8.6.6) id AAA05109 for current-outgoing; Tue, 13 Jun 1995 00:32:39 -0700 Received: from mpp.com ([204.157.201.242]) by freefall.cdrom.com (8.6.10/8.6.6) with ESMTP id AAA05094 for ; Tue, 13 Jun 1995 00:32:35 -0700 Received: (from mpp@localhost) by mpp.com (8.6.11/8.6.9) id CAA03409; Tue, 13 Jun 1995 02:29:53 -0500 From: Mike Pritchard Message-Id: <199506130729.CAA03409@mpp.com> Subject: Re: GENERIC kernel & some basic UNIX pointers To: bde@zeta.org.au (Bruce Evans) Date: Tue, 13 Jun 1995 02:29:53 -0500 (CDT) Cc: roberto@blaise.ibp.fr, wollman@halloran-eldar.lcs.mit.edu, current@FreeBSD.ORG In-Reply-To: <199506130350.NAA06987@godzilla.zeta.org.au> from "Bruce Evans" at Jun 13, 95 01:50:07 pm X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 1332 Sender: current-owner@FreeBSD.ORG Precedence: bulk > The kernel mode ppp has a hack for low ping latency. This saves an average > of 5ms per end. Again, this should have little effect for large transmissions > if everything is streaming properly. > > kernel ppp is inefficiently programmed. On a 486DX2/66 with a 16550 UART, > the input overheads for 115200 bps are approximately: > > termios(raw) 6.3% > cslip 7% > ppp 9% > > These overheads include delivery of packets to an application that throws > the packets away. About 3% of each overhead is for the lowest level of > the driver (which handles interrupts and stores the input in a buffer). > Thus for ppp, about 66% of the overhead is for the protocol and for > delivery of packets to the user. It might be possibele for a user mode > ppp to improve on this, but not by much since it has to pay for the > termios(raw) protocol and packet delivery. > > Bruce I guess that I will have to run some user-mode/kernel-mode tests myself. If it really does turn out that the kernel-mode ppp interface is poorly implemented, I could probably be talked into trying to make it better, especially since I'm stuck with a ppp-only ISP now. If anyone has any suggestions towards this goal, let me know. -- Mike Pritchard mpp@legarto.minn.net "Go that way. Really fast. If something gets in your way, turn"