| Message ID | 1315915334.6300.15.camel@marge.simson.net |
|---|---|
| State | New |
| Headers | show |
On Tue, Sep 13, 2011 at 02:02:14PM +0200, Mike Galbraith wrote: > 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. Very good -- some comments below. I had to hand-apply this due to conflicts with my current patch stack: https://github.com/paulmckrcu/linux > 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 <efault@gmx.de> > > --- > 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 <linux/delay.h> > #include <linux/stop_machine.h> > > +#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; This makes sense, and I have merged it into your previous patch. > 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; This is broken -- the per-node kthread runs at RT prio 99, but we usually would not want to boost that high. 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? > 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); > >
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. -Mike
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
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 <linux/delay.h> #include <linux/stop_machine.h> +#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);