From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759522AbYBFGhT (ORCPT ); Wed, 6 Feb 2008 01:37:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752103AbYBFGhH (ORCPT ); Wed, 6 Feb 2008 01:37:07 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:32781 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752052AbYBFGhF (ORCPT ); Wed, 6 Feb 2008 01:37:05 -0500 Subject: Re: RT scheduler config, suggestions and questions From: Peter Zijlstra To: Max Krasnyanskiy Cc: Steven Rostedt , Ingo Molnar , LKML In-Reply-To: <47A8F328.5070107@qualcomm.com> References: <47A8F328.5070107@qualcomm.com> Content-Type: text/plain Date: Wed, 06 Feb 2008 07:36:55 +0100 Message-Id: <1202279815.19243.34.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.21.90 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-02-05 at 15:37 -0800, Max Krasnyanskiy wrote: > Folks, > > I just realized that in latest Linus' tree following sysctls are under SCHED_DEBUG: > sched_rt_period > sched_rt_ratio > > I do not believe that is correct. I know that we do not want to expose scheduler knobs > in general but theses are not the heuristic kind of knobs. There is no way the scheduler > can magically figure out what the correct setting should be here. Yeah, since fixed. > Also shouldn't those new RT features that recently went be configurable and _disabled_ > by default ? For example "RT watchdog" and "RT throttling" actually seem very questionable. > SCHED_FIFO is clearly defined as > " > A SCHED_FIFO process runs until either it is blocked by an I/O request, it is preempted > by a higher priority process, or it calls sched_yield(2). > " The watchdog is disabled by default, the bandwidth is .95s every 1s, which is mainly a safe-guard against run-away real-time tasks. As long as real-time usage stays within those limits nothing happens. If you don't like it set sched_rt_runtime [*] to -1. [*] provided in the interface changes posted a few days ago. > Both the watchdog and the throttling are clearly braking that rule. I think it's good to have > those features but not enabled by default and certainly not with sysctls that disable them > hidden under debugging. > How about this: > - We introduce Kconfig options for them ? I don't see why this would be needed. > - Expose all rt sysctls outside of #ifdef DEBUG Already did this somewhere along the line. > btw I can see "watchdog" being very useful to catch hard-RT tasks that exceed the deadline. > But's it gotta be per thread. It is. > Single setting per user is not enough. Unless a use has a single RT task. ?