Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756229Ab2FNPDw (ORCPT ); Thu, 14 Jun 2012 11:03:52 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:39453 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756075Ab2FNPDv (ORCPT ); Thu, 14 Jun 2012 11:03:51 -0400 Date: Thu, 14 Jun 2012 08:01:18 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: LKML , Peter Zijlstra , Ingo Molnar , "Srivatsa S. Bhat" , Rusty Russell , Tejun Heo Subject: Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads Message-ID: <20120614150118.GC2458@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12061415-7606-0000-0000-0000011F06C3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2157 Lines: 50 On Thu, Jun 14, 2012 at 04:12:14PM +0200, Thomas Gleixner wrote: > On Thu, 14 Jun 2012, Thomas Gleixner wrote: > > On Thu, 14 Jun 2012, Thomas Gleixner wrote: > > > > > On Thu, 14 Jun 2012, Paul E. McKenney wrote: > > > > On Thu, Jun 14, 2012 at 01:20:39PM +0200, Thomas Gleixner wrote: > > > > > I gave it a quick shot, but I was not able to reproduce the hang yet. > > > > > > > > Really? I have a strictly Western-Hemisphere bug? ;-) > > > > > > I guess I need to fire up rcu torture to make it surface. > > > > > > > > But looking at the thread function made me look into rcu_yield() and I > > > > > really wonder what kind of drug induced that particular piece of > > > > > horror. > > > > > > > > When you are working on something like RCU priority boosting, no other > > > > drug is in any way necessary. ;-) > > > > > > And how do we protect minors from that ? > > > > > > > > I can't figure out why this yield business is necessary at all. The > > > > > commit logs are as helpful as the missing code comments :) > > > > > > > > > > I suspect that it's some starvation issue. But if we need it, then > > > > > can't we replace it with something sane like the (untested) patch > > > > > below? > > > > > > > > Yep, starvation. I will take a look at your approach after I wake > > > > up a bit more. > > > > > > Btw, if that simpler yield approach is working and I can't see why it > > > shouldn't then you can get rid of the node task as well. The only > > > purpose of it is to push up the priority of yielding tasks, right? > > > > Ah, missed that it calls rcu_initiate_boost() as well.... > > And looking further, I really don't understand why it's doing > that. That node thread is only woken by these weird yield timers. If your patch works out, it indeed might be possible to get rid of ->node_kthread_task. The ->boost_kthread_task needs to stay, however. 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/