From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <396C9188.523658B9@sangate.com> Date: Wed, 12 Jul 2000 18:40:56 +0300 From: Mark Mokryn MIME-Version: 1.0 Subject: map_user_kiobuf problem in 2.4.0-test3 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.rutgers.edu, linux-scsi@vger.rutgers.edu, linux-mm@kvack.org List-ID: Hi, Here's the scenario: 2.4.0-test3 SMP build running on a single 800MHz PIII (Dell GX-300) After obtaining a mapping to a high memory region (i.e. either PCI memory or physical memory reserved by passing mem=XXX to the kernel at boot), I am trying to write a raw device with data in the mapped region. This fails, with map_user_kiobuf spitting out "Mapped page missing" The raw write works, of course, if the mapping is to a kmalloc'ed buffer. I have tried the above with 2.2.14 SMP, and it works, so something in 2.4 is broken. 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%! This is very strange, since if the transfer rate was for some unknown reason lower in the case of PCI (vs. high physical memory), then one would expect the CPU utilization to be even lower, since the adapter performs DMA. But instead, the CPU is sweating... So, it appears that there's a problem in 2.2.14 as well, when the mapping is to PCI space... Additionally, the max transfer rate of 8MB/s seems rather slow - don't know why yet... -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/