From owner-freebsd-current Tue Oct 13 11:21:30 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id LAA25479 for freebsd-current-outgoing; Tue, 13 Oct 1998 11:21:30 -0700 (PDT) (envelope-from owner-freebsd-current@FreeBSD.ORG) Received: from awfulhak.org (awfulhak.force9.co.uk [195.166.136.63]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id LAA25423 for ; Tue, 13 Oct 1998 11:21:24 -0700 (PDT) (envelope-from brian@Awfulhak.org) Received: from woof.lan.awfulhak.org (brian@woof.lan.awfulhak.org [172.16.0.7]) by awfulhak.org (8.8.8/8.8.8) with ESMTP id TAA22700; Tue, 13 Oct 1998 19:21:03 +0100 (BST) (envelope-from brian@Awfulhak.org) Received: from woof.lan.awfulhak.org (brian@localhost [127.0.0.1]) by woof.lan.awfulhak.org (8.9.1/8.9.1) with ESMTP id JAA00674; Tue, 13 Oct 1998 09:43:48 +0100 (BST) (envelope-from brian@woof.lan.awfulhak.org) Message-Id: <199810130843.JAA00674@woof.lan.awfulhak.org> X-Mailer: exmh version 2.0.2 2/24/98 To: Bruce Evans cc: brian@Awfulhak.org, kjc@csl.sony.co.jp, current@FreeBSD.ORG Subject: Re: Improper sharing of modem bandwidth In-reply-to: Your message of "Tue, 13 Oct 1998 15:41:01 +1000." <199810130541.PAA12787@godzilla.zeta.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Tue, 13 Oct 1998 09:43:48 +0100 From: Brian Somers Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > >Surely, once the packet queueing delay is reduced, we need to reduce > >the tty delay. The current kernel doesn't have ioctls for the > >buffer size but slip uses a smaller tty buffer and has a better > >response time than ppp. > > User ppp is behind a _lot_ of output buffering, including (at speeds >= > 57600 Kbps) a 4KB tty buffer (up from 2KB in FreeBSD-2.2). Perhaps the > increase from 2KB to 4KB is especially significant when the MTU is 1500. Heh, I *assumed* (yes, I know) that the tty buffer was around 128 or 256 bytes, but definitely less than 1500 !!! So in practice, in 3.0 with a 1500 MTU, we won't be able to skip ahead of the 4096 bytes (assuming a busy link) at the front of the queue. Without suspend/resume, we'll have to wait behind up to 1500 additional bytes (750 avg) and with suspend/resume we'd wait behind an additional 0 bytes and send 1 or 2 additional HDLC escape codes to do the suspend/resume. This gives a ~15% latency improvement, which isn't brilliant, but is better than nothing. If there was an ioctl to change the usable tty buffer size to less than 4k, ppp could set it to ``whatever the MTU is'' and get quite a reasonable interactive performance gain. > Kernel ppp doesn't have this problem. Kernel ppp also has a fast path > for incoming packets to avoid the average 5ms latency for polling the > pseudo-DMA input buffer. This only seems to be important for local > connections. > > Bruce -- Brian , , Don't _EVER_ lose your sense of humour.... To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message