From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from penguin.netx4.com (embeddededge.com [209.113.146.155]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 4C8CF6801D for ; Tue, 23 Aug 2005 03:13:27 +1000 (EST) In-Reply-To: <4309E2AC.9080404@icarus.com> References: <4309E2AC.9080404@icarus.com> Mime-Version: 1.0 (Apple Message framework v622) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: <20d4aca8d8032c5762deb047185d2c6e@embeddededge.com> From: Dan Malek Date: Mon, 22 Aug 2005 13:09:57 -0400 To: Stephen Williams Cc: linuxppc-embedded@ozlabs.org Subject: Re: mmap nocache on PPC, 2.4 List-Id: Linux on Embedded PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Aug 22, 2005, at 10:35 AM, Stephen Williams wrote: > In an embedded system, I want a big chunk of virtual memory in the > user process to be uncached. Why? What processor it this? Who else touches this memory? > .... I've created a virtual device driver that > has this mmap method: Even if this did what you thought it should, I'm not sure you would be happy with the results. The challenge is ensuring anyone that touches these physical pages also does so uncached. Depending upon the processor, this isn't something that is trivial to change in the kernel, since we always map all of memory as efficiently as possible with a cached mapping. The caching of memory has many desirable performance side effects, making the trade off the manage coherency in software if needed an overall system gain. Thanks. -- Dan