From owner-freebsd-hackers Sun Dec 7 20:25:02 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id UAA26519 for hackers-outgoing; Sun, 7 Dec 1997 20:25:02 -0800 (PST) (envelope-from owner-freebsd-hackers) Received: from anlsun.ebr.anlw.anl.gov (anlsun.ebr.anlw.anl.gov [141.221.1.2]) by hub.freebsd.org (8.8.7/8.8.7) with SMTP id UAA26506 for ; Sun, 7 Dec 1997 20:24:53 -0800 (PST) (envelope-from cmott@srv.net) Received: from darkstar.home (ras704.srv.net [205.180.127.204]) by anlsun.ebr.anlw.anl.gov (8.6.11/8.6.11) with SMTP id VAA10543; Sun, 7 Dec 1997 21:24:45 -0700 Date: Sun, 7 Dec 1997 21:24:10 -0700 (MST) From: Charles Mott X-Sender: cmott@darkstar.home To: John-Mark Gurney cc: Brad Karp , pst@shockwave.com, freebsd-hackers@FreeBSD.ORG, karp@dominator.eecs.harvard.edu Subject: Re: FreeBSD Metricom driver: I wrote one in September... In-Reply-To: <19971207193932.61833@hydrogen.nike.efn.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk > > My driver is written over the IP tunnel (tun), and is completely portable > > (no #ifdefs, even) between FreeBSD and NetBSD (I use it on both systems). It > > does neighbor discovery, dynamically handles IP-to-MAC mapping for the radios > > (with no centralized ARP server, despite the non-broadcast nature of Metricom's > > radios), and works very well, overall. > > hmmm... tun is nice for portability, but it still doesn't match the > performance of a kernel land driver... the extra context switches > do impact performance... a ping to a remote host has to traverse the > kernel/userland boundary three times when pinging a remote host... > (ping->kernel->tunnel->output to device/network)... On late model Pentiums, I think kernel-user context switch is down to about 5 microseconds (it's about 60 microseconds on my 386) for an individual system call. However, maybe one or two OS quantums (10 milliseconds) are added for hauling the packets around. Is this the problem you are talking about? (I don't know the answer and am trying ot understand system timing better). Charles Mott