From mboxrd@z Thu Jan 1 00:00:00 1970 From: Armin Steinhoff Subject: Re: PREEMPT_RT patch vs RTAI/Xenomai Date: Fri, 14 May 2010 11:34:47 +0200 Message-ID: <4BED1937.6080907@steinhoff.de> References: <1273680443.27703.33.camel@gandalf.stny.rr.com> <4BEBB1C8.90606@steinhoff.de> <20100513175842.GN6055@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-rt-users@vger.kernel.org To: Robert Schwebel Return-path: Received: from moutng.kundenserver.de ([212.227.17.10]:61402 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752194Ab0ENKXw (ORCPT ); Fri, 14 May 2010 06:23:52 -0400 In-Reply-To: <20100513175842.GN6055@pengutronix.de> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Robert Schwebel wrote: > On Thu, May 13, 2010 at 10:01:12AM +0200, Armin Steinhoff wrote: > >> I did a test with user space based CAN driver. >> > The Linux CAN interface is SocketCAN. Do you see a usecase where this > doesn't fit? > IMHO, the SocketCAN interface is simply an overkill for the handling of small CAN messages. I estimate that the amount of executed code for handling of a single CAN frame is much bigger as the frame itself :) Every read and write action creates context switches ... This is not the case with the user space based driver. Same story with our PROFIBUS-DP drivers ... >> Already the standard distribution of SUSE 11.2 (non RT) was able to >> handle 1000 frames per seconds sent by a QNX6 machine !! >> > > Realtime != fast. > But a small response time is a technological requirement in order to meet deadlines. The standard kernel is a _good base_ in order to implement predictive behavior ... this would not the case if the response time would be in the range of 100us. OK ... you can have real-time behavior with a response time of 100us .. but this would be useless for most real-time applications. >> The latency test of PREEMPT_RT shows a latency of ~10us for a >> dual-core box at 1.8GHz. >> > > It depends on the load. > It depends on the load and the used priorities. --Armin