Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756357Ab2FNPqN (ORCPT ); Thu, 14 Jun 2012 11:46:13 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:48750 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756000Ab2FNPqM (ORCPT ); Thu, 14 Jun 2012 11:46:12 -0400 Date: Thu, 14 Jun 2012 08:45:56 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Thomas Gleixner , LKML , Ingo Molnar , "Srivatsa S. Bhat" , Rusty Russell , Tejun Heo Subject: Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads Message-ID: <20120614154556.GD2458@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1339685789.2559.37.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12061415-4242-0000-0000-000001F7CB7C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1147 Lines: 28 On Thu, Jun 14, 2012 at 04:56:29PM +0200, 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? In -rt, yes, but in mainline, ksoftirqd does not run at RT prio, right? > Also, no its not quite like the throttling, that really idles the cpu > even if there's no SCHED_OTHER tasks to run. Agreed, not -exactly- like throttling, but it has a broadly similar goal, namely to prevent a given type of processing from starving everything else in the system. That said, why does throttling idle the CPU even if there is no other SCHED_OTHER tasks to run? Thanx, Paul -- 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/