From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932641Ab1IMUvH (ORCPT ); Tue, 13 Sep 2011 16:51:07 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:45882 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932446Ab1IMUvE (ORCPT ); Tue, 13 Sep 2011 16:51:04 -0400 Date: Tue, 13 Sep 2011 13:50:55 -0700 From: "Paul E. McKenney" To: Mike Galbraith Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org Subject: Re: [PATCH tip/core/rcu 44/55] rcu: wire up RCU_BOOST_PRIO for rcutree Message-ID: <20110913205055.GF3301@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110906180015.GA2560@linux.vnet.ibm.com> <1315332049-2604-44-git-send-email-paulmck@linux.vnet.ibm.com> <1315915334.6300.15.camel@marge.simson.net> <20110913153413.GB2416@linux.vnet.ibm.com> <1315929858.6312.16.camel@marge.simson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1315929858.6312.16.camel@marge.simson.net> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 13, 2011 at 06:04:18PM +0200, Mike Galbraith wrote: > On Tue, 2011-09-13 at 08:34 -0700, Paul E. McKenney wrote: > > On Tue, Sep 13, 2011 at 02:02:14PM +0200, Mike Galbraith wrote: > > > > @@ -1608,7 +1618,7 @@ static int rcu_node_kthread(void *arg) > > > continue; > > > } > > > per_cpu(rcu_cpu_has_work, cpu) = 1; > > > - sp.sched_priority = RCU_KTHREAD_PRIO; > > > + sp.sched_priority = current->rt_priority; > > > > This is broken -- the per-node kthread runs at RT prio 99, but we usually > > would not want to boost that high. > > Ouch, right. My userland sets things on boot, so it works. ;-) > > Seems like we should have a global variable that tracks the current > > priority. This global variable could then be set in a manner similar > > to the softirq priorities -- or, perhaps better, simply set whenever > > the softirq priority is changed. > > > > Thoughts? > > RCU threads would have to constantly watch for user priority changes on > their own, and update private data methinks. I believe that we are going to need some sort of -rt-specific handling of the RCU boost priority in the short term. Though maybe I could think about getting runtime modification into mainline as well -- but it would be different that -rt for a bit. Thanx, Paul