From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 13 May 2001 11:55:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 13 May 2001 11:54:57 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:26668 "EHLO flinx.biederman.org") by vger.kernel.org with ESMTP id ; Sun, 13 May 2001 11:54:44 -0400 To: Jamie Lokier Cc: "Richard B. Johnson" , Alan Cox , alexander.eichhorn@rz.tu-ilmenau.de, linux-kernel@vger.kernel.org Subject: Re: [Question] Explanation of zero-copy networking In-Reply-To: <20010508091811.C17720@pcep-jamie.cern.ch> From: ebiederm@xmission.com (Eric W. Biederman) Date: 09 May 2001 09:13:36 -0600 In-Reply-To: Jamie Lokier's message of "Tue, 8 May 2001 09:18:11 +0200" Message-ID: User-Agent: Gnus/5.0803 (Gnus v5.8.3) Emacs/20.5 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Jamie Lokier writes: > Richard B. Johnson wrote: > > However, PCI to memory copying runs at about 300 megabytes per > > second on modern PCs and memory to memory copying runs at over 1,000 > > megabytes per second. In the future, these speeds will increase. > > That would be "big expensive modern PCs" then. Our clusters of 700MHz > boxes are strictly limited to 132 megabytes per second over PCI... 300 Megabytes per second is definitely an odd number for a PCI bus. But 132 Megabytes per second is actually high, the continuous burst speeds are: 32bit 33Mhz: 33*1000*1000*32/(1024*1024*8) = 125.8 Megabytes/second 64bit 33Mhz: 33*1000*1000*64/(1024*1024*8) = 251.7 Megabytes/second 32bit 66Mhz: 66*1000*1000*32/(1024*1024*8) = 251.7 Megabytes/second 64bit 66Mhz: 66*1000*1000*64/(1024*1024*8) = 503.4 Megabytes/second The possibility of getting a continuous bursts is actually low, if nothing else you have an interrupt acknowledgement 100 times per second. But if you are pushing the bus it should deliver close to it's burst potential. But the ISA traffic doing subtractive decode can be nasty because you get 4 PCI cycles before you even get acknowledgement from the PCI/ISA bridge that you there is something to transfer to. Eric