From owner-freebsd-questions Thu Mar 7 20:49:40 1996 Return-Path: owner-questions Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id UAA09800 for questions-outgoing; Thu, 7 Mar 1996 20:49:40 -0800 (PST) Received: from ns.okbmei.msk.su (ns.okbmei.msk.su [194.190.170.40]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id UAA09789 for ; Thu, 7 Mar 1996 20:49:35 -0800 (PST) Received: from kiae.UUCP by ns.okbmei.msk.su with UUCP id AA02307 (5.67c8/IDA-1.5); Fri, 8 Mar 1996 07:40:24 +0300 Received: from freefall.FreeBSD.ORG by sequent.kiae.su with SMTP id AA19816 (5.65.kiae-2 for ); Fri, 8 Mar 1996 07:28:27 +0300 Received: from localhost (daemon@localhost) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id NAA13504 Thu, 7 Mar 1996 13:48:48 -0800 (PST) Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id NAA12934 for questions-outgoing; Thu, 7 Mar 1996 13:46:39 -0800 (PST) Received: from labinfo.iet.unipi.it (labinfo.iet.unipi.it [131.114.9.5]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id NAA12872 for ; Thu, 7 Mar 1996 13:46:29 -0800 (PST) Received: from localhost (luigi@localhost) by labinfo.iet.unipi.it (8.6.5/8.6.5) id WAA11583; Thu, 7 Mar 1996 22:41:04 +0100 From: Luigi Rizzo Message-Id: <199603072141.WAA11583@labinfo.iet.unipi.it> Subject: Re: Bad Ethernet cards To: terry@lambert.org (Terry Lambert) Date: Thu, 7 Mar 1996 22:41:03 +0100 (MET) Cc: terry@lambert.org, wollman@lcs.mit.edu, questions@FreeBSD.org In-Reply-To: <199603072047.NAA14745@phaeton.artisoft.com> from "Terry Lambert" at Mar 7, 96 01:47:01 pm X-Mailer: ELM [version 2.4 PL23] Content-Type: text X-Charset: KOI8-R X-Char-Esc: 29 Sender: owner-questions@FreeBSD.org Precedence: bulk > > I did my computation as follows: assume the CPU has to transfer 1MB/s > > from the board. Say the available bandwidth on the PCI bus, doing > > programmed I/O, is X MB/s. Then the CPU uses 1/X of its time just to > > transfer that 1MB/s. For X=20, that makes 5% of the CPU time > > unavailable for other things. Anything wrong ? > > The CPU spends 1/X * clock_differential_for_bus_access of its time; > it will be in "bus wait" on clock_differential_for_bus_access - 1 > of those clocks that it ordinarily would be using to run instructions > in its L1 cache. The bandwidth I call "X" is the available bandwidth in accessing that particular device, which varies from device to device. What you call X is probably something diffetent. > I intensely dislike clock multiplied chips for precisely this reason; If you have to drive the I/O pins at 200 MHz instead of 66, then your CPU will likely consume 100W or more, provided you are able to make it work reliably and cool it down to a reasonable temperature. I suppose the little daemon would feel very comfortable on such a CPU :) Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================