Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753903AbbKQNtq (ORCPT ); Tue, 17 Nov 2015 08:49:46 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:51631 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752068AbbKQNto (ORCPT ); Tue, 17 Nov 2015 08:49:44 -0500 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Tue, 17 Nov 2015 05:49:46 -0800 From: "Paul E. McKenney" To: Jacob Pan Cc: Peter Zijlstra , Arjan van de Ven , Josh Triplett , Thomas Gleixner , Ingo Molnar , John Stultz , LKML , Srinivas Pandruvada , Len Brown , Rafael Wysocki , Eduardo Valentin , Paul Turner Subject: Re: [PATCH 2/4] timer: relax tick stop in idle entry Message-ID: <20151117134946.GT5184@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20151116135126.5a50e45d@icelake> <20151116223210.GA21522@cloud> <20151116232640.GM5184@linux.vnet.ibm.com> <20151117014103.GA6629@x> <20151117025342.GP5184@linux.vnet.ibm.com> <564A978A.8060905@linux.intel.com> <20151117050403.GQ5184@linux.vnet.ibm.com> <20151117102449.GR3816@twins.programming.kicks-ass.net> <20151117045721.2c565e42@yairi> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151117045721.2c565e42@yairi> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15111713-0017-0000-0000-00000F950EEA Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2055 Lines: 45 On Tue, Nov 17, 2015 at 04:57:21AM -0800, Jacob Pan wrote: > On Tue, 17 Nov 2015 11:24:49 +0100 > Peter Zijlstra wrote: > > > On Mon, Nov 16, 2015 at 09:04:03PM -0800, Paul E. McKenney wrote: > > > On Mon, Nov 16, 2015 at 06:57:14PM -0800, Arjan van de Ven wrote: > > > > On 11/16/2015 6:53 PM, Paul E. McKenney wrote: > > > > >Fair point. When in the five-jiffy throttling state, what can > > > > >wake up a CPU? In an earlier version of this proposal, the > > > > >answer was "nothing", but maybe that has changed. > > > > > > > > device interrupts are likely to wake the cpus. > > > > > > OK, that I cannot help you with. But presumably if the interrupt > > > handler does a wakeup (or similar), that is deferred to the end of > > > the throttling interval? Timers are also deferred, including > > > hrtimers? > > > > This throttling thing only throttles 'normal' tasks, real-time tasks > > will still run. Heh! Then RCU will be delayed or not based on the priority of the grace-period kthreads and softirqd. ;-) In addition, this does sound like an excellent test for priority-inversion situations that might otherwise go unnoticed on overprovisioned systems. That said, I would expect many types of real-time systems to configure voltage, frequency, and cooling so as to avoid thermal throttling. > As an optimization or option, it might be useful to further defer the > next timer interrupt if it falls within the idle injection period. But > I guess we don't know if that timer belongs to a normal task or rt. > Also we there could be more than one 'next' timer interrupts fall into > that injection idle period. Understood. This brings me back to my recommendation that throttling select RCU_FAST_NO_HZ unless RCU_NOCB_CPU_ALL is already set. 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/