From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756704AbZHFUPi (ORCPT ); Thu, 6 Aug 2009 16:15:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756678AbZHFUPh (ORCPT ); Thu, 6 Aug 2009 16:15:37 -0400 Received: from mail2.shareable.org ([80.68.89.115]:59825 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756185AbZHFUPg (ORCPT ); Thu, 6 Aug 2009 16:15:36 -0400 Date: Thu, 6 Aug 2009 21:15:27 +0100 From: Jamie Lokier To: David Xiao Cc: Laurent Pinchart , Ben Dooks , Hugh Dickins , Robin Holt , "linux-kernel@vger.kernel.org" , v4l2_linux , "linux-arm-kernel@lists.arm.linux.org.uk" Subject: Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Is get_user_pages() enough to prevent pages from being swapped out ?") Message-ID: <20090806201527.GA8725@shareable.org> References: <200908061208.22131.laurent.pinchart@ideasonboard.com> <20090806114619.GW2080@trinity.fluff.org> <200908061506.23874.laurent.pinchart@ideasonboard.com> <1249584374.29182.20.camel@david-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1249584374.29182.20.camel@david-laptop> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org David Xiao wrote: > Another approach is working from a different direction: the kernel > allocates the non-cached buffer and then mmap() into user space. I have > done that in similar situation to try to achieve "zero-copy". open(O_DIRECT) does DMA to arbitrary pages allocated by userspace, and O_DIRECT is used by some important applications, so the problem still needs to be solved in general. -- Jamie