Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754169Ab2FNPHe (ORCPT ); Thu, 14 Jun 2012 11:07:34 -0400 Received: from www.linutronix.de ([62.245.132.108]:58346 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753249Ab2FNPHd (ORCPT ); Thu, 14 Jun 2012 11:07:33 -0400 Date: Thu, 14 Jun 2012 17:07:30 +0200 (CEST) From: Thomas Gleixner To: Peter Zijlstra cc: paulmck@linux.vnet.ibm.com, LKML , Ingo Molnar , "Srivatsa S. Bhat" , Rusty Russell , Tejun Heo Subject: Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads In-Reply-To: <1339685789.2559.37.camel@twins> Message-ID: References: <20120613102823.373180763@linutronix.de> <20120613105815.206105518@linutronix.de> <20120613185748.GF2427@linux.vnet.ibm.com> <20120613191745.GG2427@linux.vnet.ibm.com> <20120613204725.GA9858@linux.vnet.ibm.com> <20120614045125.GA30257@linux.vnet.ibm.com> <20120614125939.GC2443@linux.vnet.ibm.com> <1339678887.2559.30.camel@twins> <20120614144734.GA2458@linux.vnet.ibm.com> <1339685789.2559.37.camel@twins> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1047 Lines: 28 On Thu, 14 Jun 2012, Peter Zijlstra wrote: > On Thu, 2012-06-14 at 07:47 -0700, Paul E. McKenney wrote: > > RCU callback processing consumes the entire CPU in RCU_BOOST case where > > processing runs at real-time priority. This is analogous to RT throttling > > in the scheduler. > > But previously we can in non-preemptible softirq context, why would if > behave differently when done from a RT task? softirqs are different. They loop ten times and then wake ksoftirqd which runs with sched_other. Though that's wonky, because if an interrupt arrives before ksoftirqd can take over we loop another 10 times in irq_exit(). Rinse and repeat..... And the main difference is that the scheduler does not yell on the softirq context, but it yells when an rt task monopolizes the cpu. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/