From mboxrd@z Thu Jan 1 00:00:00 1970 From: Armin Steinhoff Subject: Re: I/O operations priority in RTOS Date: Mon, 06 Jun 2011 09:41:58 +0200 Message-ID: <4DEC84C6.4090702@steinhoff.de> References: <4DEA1BA9.7020303@unican.es> <4DEA1F22.6000603@unican.es> <20110604234214.GA30640@opentech.at> <4DEB427F.9020104@steinhoff.de> <20110605092854.GA7576@opentech.at> <4DEB5015.7070601@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Nicholas Mc Guire , Monica Puig-Pey , linux-rt-users@vger.kernel.org To: Jan Kiszka Return-path: Received: from moutng.kundenserver.de ([212.227.126.186]:50772 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756720Ab1FFHc0 (ORCPT ); Mon, 6 Jun 2011 03:32:26 -0400 In-Reply-To: <4DEB5015.7070601@web.de> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Jan Kiszka wrote: > On 2011-06-05 11:28, Nicholas Mc Guire wrote: >> On Sun, 05 Jun 2011, Armin Steinhoff wrote: >> >>> Nicholas Mc Guire wrote: >>>> On Sat, 04 Jun 2011, Monica Puig-Pey wrote: >>>> >>>>> Hello, >>>>> I'm studying how to develop drivers in a real time OS and how do they >>>>> work. I'm using Ubuntu 10.04 with the 2.6.31-11-rt patch installed. >>>>> I would like to know the priority when executing open(), read(), write() >>>>> and close() operations. >>>>> In my example the thread which is using the driver runs with 10 RTPRIO, >>>>> but I don't know what happens in kernel context with the priority when >>>>> running the I/O operations. >>>>> Thank you for your help, I don't know where to learn about this. >>>>> >>>> [] >>>> Also when using bottom half mechanisms you need to take into account the >>>> priority of the kernel thread that manages the defered work items, so >>>> rt-drivers may have a different structure than normal drivers. >>> That's the reason why I prefer UIO based user space drivers ! >>> >> ...and how to resolve DMA ? if DMA were resolved cleanly I would agree. > Regarding that limitation, there is some hope: "next-generation" UIO is > called VFIO. I found in a posting about VFIO that " ioctls are used for all the basic interactions" ... that means VFIO works with a lot of context switches. That's not the case with UIO. So why should VFIO be a mainline approach or next generation UIO at all? --Armin