Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 6 Apr 2001 13:31:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 6 Apr 2001 13:31:18 -0400 Received: from delta.ds2.pg.gda.pl ([213.192.72.1]:33262 "EHLO delta.ds2.pg.gda.pl") by vger.kernel.org with ESMTP id ; Fri, 6 Apr 2001 13:31:06 -0400 Date: Fri, 6 Apr 2001 19:07:45 +0200 (MET DST) From: "Maciej W. Rozycki" To: "Eric W. Biederman" cc: Geert Uytterhoeven , James Simmons , Alan Cox , Linux Fbdev development list , Linux Kernel Mailing List Subject: Re: [Linux-fbdev-devel] Re: fbcon slowness [was NTP on 2.4.2?] In-Reply-To: Message-ID: Organization: Technical University of Gdansk 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 On 5 Apr 2001, Eric W. Biederman wrote: > The point is on the Alpha all ram is always cached, and i/o space is > completely uncached. You cannot do write-combing for video card You don't want to cache fb memory, do you? All you want is write combining and you achieve it with memory barriers. You write to fb memory space whatever you need to and write buffers actually deliver data to fb memory whenever the bus is idle or they get filled up. When you finally decide you wrote all data and you want ensure it actually reaches the fb memory before you perform an operation (say you send a command to fb's support circuitry) you issue a write memory barrier. Or a memory barrier, if you want ensure the data reaches the fb memory ASAP. In other words, you have write-combining by default and request write-through explicitly. > memory. Memory barriers are a separate issue. On the alpha the > natural way to implement it would be in the page table fill code. Please forgive me -- I can't see how this is related to write combining. > Memory barriers are o.k. but the really don't help the case when what > you want to do is read the latest value out of a pci register. They do -- you issue an mb and you are sure all pending writes reached the involved PCI hw. -- + Maciej W. Rozycki, Technical University of Gdansk, Poland + +--------------------------------------------------------------+ + e-mail: macro@ds2.pg.gda.pl, PGP key available + - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/