From owner-freebsd-hackers Wed Feb 17 14:44:52 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [209.157.86.2]) by hub.freebsd.org (Postfix) with ESMTP id 57E31112D4 for ; Wed, 17 Feb 1999 14:44:18 -0800 (PST) (envelope-from dillon@apollo.backplane.com) Received: (from dillon@localhost) by apollo.backplane.com (8.9.3/8.9.1) id OAA11578; Wed, 17 Feb 1999 14:44:15 -0800 (PST) (envelope-from dillon) Date: Wed, 17 Feb 1999 14:44:15 -0800 (PST) From: Matthew Dillon Message-Id: <199902172244.OAA11578@apollo.backplane.com> To: "John S. Dyson" Cc: dyson@iquest.net, tlambert@primenet.com, toasty@home.dragondata.com, mike@smith.net.au, hackers@FreeBSD.ORG Subject: Re: vm_page_zero_fill References: <199902172139.QAA70278@y.dyson.net> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG :> :> This is robbing Peter to pay Paul; in a way. The base assumption :> that you are hiding is that you aren't constrained by memory :> bandwidth. This isn't true if you are nearly saturating a PCI :> bus with 4 BT848's (to pick the highest memory bandwidth application :> I know about). :> :I just realized something: : : Memory bandwidth is >> PCI bandwidth on good designs. I believe :that the PCI and memory busses are decoupled on at least some X86 machines. : :-- :John | Never try to teach a pig to sing, :dyson@iquest.net | it makes one look stupid :jdyson@nc.com | and it irritates the pig. Main memory and the PCI bus are decoupled and buffered with FIFOs on all designs that I know of. That's what all those burst and write posting options are in the chipset BIOS. This is why you want to use DMA... it won't (much) stall main memory or the cpu while transfering data to or from the PCI bus. -Matt Matthew Dillon To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message