From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264121AbTDOV55 (for ); Tue, 15 Apr 2003 17:57:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264122AbTDOV55 (for ); Tue, 15 Apr 2003 17:57:57 -0400 Received: from c-97a870d5.037-69-73746f23.cust.bredbandsbolaget.se ([213.112.168.151]:61312 "EHLO zaphod.guide") by vger.kernel.org with ESMTP id S264121AbTDOV54 (for ); Tue, 15 Apr 2003 17:57:56 -0400 To: Alan Cox Cc: Linux Kernel Mailing List Subject: Re: DMA transfers in 2.5.67 References: <1050438684.28586.8.camel@dhcp22.swansea.linux.org.uk> <1050439715.28586.17.camel@dhcp22.swansea.linux.org.uk> From: mru@users.sourceforge.net (=?iso-8859-1?q?M=E5ns_Rullg=E5rd?=) Date: 16 Apr 2003 00:09:00 +0200 In-Reply-To: <1050439715.28586.17.camel@dhcp22.swansea.linux.org.uk> Message-ID: User-Agent: Gnus/5.0808 (Gnus v5.8.8) XEmacs/21.4 (Portable Code) MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Alan Cox writes: > > It's an Alpha with 768 MB. Is it the pci_alloc_* functions you are > > referring to? I don't think they are used currently. How much memory > > can these allocate? I need chunks of up to 1 MB, not necessarily > > phycically continuous. > > > > What do those functions do that normal memory allocation does not? > > Apart from setting up sg mappings, that is. > > A normal memory allocation might not be visible from the device, however > pci_map_sg() deals with such things. What I really meant was are you > using the pci_ DMA functionality Those functions are not used at the moment, but I could change that. The question remains why DMA transfers are so slow. The memory is clearly visible from the bus. Btw, I just noticed that hard disk throughput is much lower with 2.5 than 2.4. With 2.4.21-pre5 I get ~40 MB/s, but with 2.5.67 the speed drops to 25-30 MB/s. Everything according to hdparm. Is it possible that DMA is generally slow for some reason? -- Måns Rullgård mru@users.sf.net