From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <396CE4AA.12C08C62@sangate.com> Date: Wed, 12 Jul 2000 23:35:38 +0200 From: Mark Mokryn MIME-Version: 1.0 Subject: Re: map_user_kiobuf problem in 2.4.0-test3 References: <396C9188.523658B9@sangate.com> <396C97F7.2AEE5FE7@augan.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Roman Zippel Cc: linux-kernel@vger.rutgers.edu, linux-scsi@vger.rutgers.edu, linux-mm@kvack.org List-ID: Hi again, Roman Zippel wrote: > > On another interesting note: The raw devices I'm writing to are Fibre > > Channel drives controlled by a Qlogic 2200 adapter (in 2.2.14 I'm using > > the Qlogic driver). When writing large sequential blocks to a single > > drive, I reached 8MB/s when the memory was mapped to the high reserved > > region, while CPU utilization was down to about 5%. When the mapping was > > to PCI space, I was able to write at only 4MB/s, and CPU utilization was > > up to 60%! > > The data is copied from a buffer to the pci device. DMA transfers going > directly to pci space is impossible without (small) changes to 2.2. 2.4 > has the theoretic possibility to do it and checks already for that, but > how it should be done practically I'd like to know too. Okay - if you're right, then this explains the poor performance I'm seeing for PCI-PCI raw I/O on 2.2.14... Raw I/O is senseless if bounce buffers are used. Still, raw I/O (the kiobuf stuff) seems to be quite broken on 2.4.0t3... -Mark -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux.eu.org/Linux-MM/