From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753164Ab1IMMC1 (ORCPT ); Tue, 13 Sep 2011 08:02:27 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:44524 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750815Ab1IMMCZ (ORCPT ); Tue, 13 Sep 2011 08:02:25 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX19omwQyBSVoJ5FgB3a4l0VTjwf+6mSSqnKYAwTN3c hwsq5mXCJaEkDD Subject: Re: [PATCH tip/core/rcu 44/55] rcu: wire up RCU_BOOST_PRIO for rcutree From: Mike Galbraith To: "Paul E. McKenney" 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 In-Reply-To: <1315332049-2604-44-git-send-email-paulmck@linux.vnet.ibm.com> References: <20110906180015.GA2560@linux.vnet.ibm.com> <1315332049-2604-44-git-send-email-paulmck@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Tue, 13 Sep 2011 14:02:14 +0200 Message-ID: <1315915334.6300.15.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Paul, This patch causes RCU thread priority funnies, with some help from rcun. On Tue, 2011-09-06 at 11:00 -0700, Paul E. McKenney wrote: > return 0; > @@ -1466,6 +1474,7 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg) > { > struct sched_param sp; > struct timer_list yield_timer; > + int prio = current->normal_prio; > > setup_timer_on_stack(&yield_timer, f, arg); > mod_timer(&yield_timer, jiffies + 2); There's a thinko there, prio either needs to be inverted before feeding it to __setscheduler().. or just use ->rt_priority. I did the latter, and twiddled rcun to restore it's priority instead of RCU_KTHREAD_PRIO. RCU threads now stay put. rcu: wire up RCU_BOOST_PRIO for rcutree RCU boost threads start life at RCU_BOOST_PRIO, while others remain at RCU_KTHREAD_PRIO. Adjust rcu_yield() to preserve priority across the yield, and if the node thread restores RT policy for a yielding thread, it sets priority to it's own priority. This sets the stage for user controlled runtime changes to priority in the -rt tree. While here, change thread names to match other kthreads. Signed-off-by: Mike Galbraith --- kernel/rcutree.c | 2 -- kernel/rcutree_plugin.h | 22 ++++++++++++++++------ 2 files changed, 16 insertions(+), 8 deletions(-) Index: linux-3.0-tip/kernel/rcutree.c =================================================================== --- linux-3.0-tip.orig/kernel/rcutree.c +++ linux-3.0-tip/kernel/rcutree.c @@ -128,8 +128,6 @@ static void rcu_node_kthread_setaffinity static void invoke_rcu_core(void); static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); -#define RCU_KTHREAD_PRIO 1 /* RT priority for per-CPU kthreads. */ - /* * Track the rcutorture test sequence number and the update version * number within a given test. The rcutorture_testseq is incremented Index: linux-3.0-tip/kernel/rcutree_plugin.h =================================================================== --- linux-3.0-tip.orig/kernel/rcutree_plugin.h +++ linux-3.0-tip/kernel/rcutree_plugin.h @@ -27,6 +27,14 @@ #include #include +#define RCU_KTHREAD_PRIO 1 + +#ifdef CONFIG_RCU_BOOST +#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO +#else +#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO +#endif + /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary. If you like #ifdef, you @@ -1345,13 +1353,13 @@ static int __cpuinit rcu_spawn_one_boost if (rnp->boost_kthread_task != NULL) return 0; t = kthread_create(rcu_boost_kthread, (void *)rnp, - "rcub%d", rnp_index); + "rcub/%d", rnp_index); if (IS_ERR(t)) return PTR_ERR(t); raw_spin_lock_irqsave(&rnp->lock, flags); rnp->boost_kthread_task = t; raw_spin_unlock_irqrestore(&rnp->lock, flags); - sp.sched_priority = RCU_KTHREAD_PRIO; + sp.sched_priority = RCU_BOOST_PRIO; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ return 0; @@ -1446,6 +1454,7 @@ static void rcu_yield(void (*f)(unsigned { struct sched_param sp; struct timer_list yield_timer; + int prio = current->rt_priority; setup_timer_on_stack(&yield_timer, f, arg); mod_timer(&yield_timer, jiffies + 2); @@ -1453,7 +1462,8 @@ static void rcu_yield(void (*f)(unsigned sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); set_user_nice(current, 19); schedule(); - sp.sched_priority = RCU_KTHREAD_PRIO; + set_user_nice(current, 0); + sp.sched_priority = prio; sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); del_timer(&yield_timer); } @@ -1562,7 +1572,7 @@ static int __cpuinit rcu_spawn_one_cpu_k if (!rcu_scheduler_fully_active || per_cpu(rcu_cpu_kthread_task, cpu) != NULL) return 0; - t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu); + t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc/%d", cpu); if (IS_ERR(t)) return PTR_ERR(t); if (cpu_online(cpu)) @@ -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; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); preempt_enable(); } @@ -1671,7 +1681,7 @@ static int __cpuinit rcu_spawn_one_node_ return 0; if (rnp->node_kthread_task == NULL) { t = kthread_create(rcu_node_kthread, (void *)rnp, - "rcun%d", rnp_index); + "rcun/%d", rnp_index); if (IS_ERR(t)) return PTR_ERR(t); raw_spin_lock_irqsave(&rnp->lock, flags);