From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261209AbVFJVGX (ORCPT ); Fri, 10 Jun 2005 17:06:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261227AbVFJVGW (ORCPT ); Fri, 10 Jun 2005 17:06:22 -0400 Received: from ppp-217-133-42-200.cust-adsl.tiscali.it ([217.133.42.200]:42562 "EHLO g5.random") by vger.kernel.org with ESMTP id S261209AbVFJVGT (ORCPT ); Fri, 10 Jun 2005 17:06:19 -0400 Date: Fri, 10 Jun 2005 23:06:14 +0200 From: Andrea Arcangeli To: Lee Revell Cc: "Paul E. McKenney" , Tim Bird , linux-kernel@vger.kernel.org, bhuey@lnxw.com, tglx@linutronix.de, karim@opersys.com, mingo@elte.hu, pmarques@grupopie.com, bruce@andrew.cmu.edu, nickpiggin@yahoo.com.au, ak@muc.de, sdietrich@mvista.com, dwalker@mvista.com, hch@infradead.org, akpm@osdl.org Subject: Re: Attempted summary of "RT patch acceptance" thread Message-ID: <20050610210614.GD6564@g5.random> References: <20050608022646.GA3158@us.ibm.com> <42A8D1F3.8070408@am.sony.com> <20050609235026.GE1297@us.ibm.com> <1118372388.32270.6.camel@mindpipe> <20050610154745.GA1300@us.ibm.com> <20050610173728.GA6564@g5.random> <1118436338.6423.48.camel@mindpipe> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1118436338.6423.48.camel@mindpipe> X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 10, 2005 at 04:45:38PM -0400, Lee Revell wrote: > AFAICT even RTAI would be affected, because X lets userspace drivers > talk directly to the hardware including wedging the PCI bus. Yes, I made the usb example exactly to show how latency bugs can be longstanding in the kernel too without requiring X or hardware bugs (this usb thing breaks kernel latency for years and yet nobody fixed it simply because it just works fine in practice, I noticed because apparently my PIT or tsc goes out of sync over time, and in turn my system time was going into the future pretty quick with HZ=1000, or I would have never noticed, of course I'm compiling the kernel with HZ=100 on that system to work around it). Those latency issues can showup in random drivers all the time, and this one was of an extreme magnitude in the millisecond range. The smaller the magnitude of the latency impact, the more frequently you should find it in drivers.