| Message ID | 1346350718-30937-2-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Aug 30, 2012 at 11:18:17AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > RCU grace-period initialization is currently carried out with interrupts > disabled, which can result in 200-microsecond latency spikes on systems > on which RCU has been configured for 4096 CPUs. This patch therefore > makes the RCU grace-period initialization be preemptible, which should > eliminate those latency spikes. Similar spikes from grace-period cleanup > and the forcing of quiescent states will be dealt with similarly by later > patches. > > Reported-by: Mike Galbraith <mgalbraith@suse.de> > Reported-by: Dimitri Sivanich <sivanich@sgi.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Does it make sense to have cond_resched() right before the continues, which lead right back up to the wait_event_interruptible at the top of the loop? Or do you expect to usually find that event already signalled? In any case: Reviewed-by: Josh Triplett <josh@joshtriplett.org> > kernel/rcutree.c | 17 ++++++++++------- > 1 files changed, 10 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index e1c5868..ef56aa3 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1069,6 +1069,7 @@ static int rcu_gp_kthread(void *arg) > * don't start another one. > */ > raw_spin_unlock_irqrestore(&rnp->lock, flags); > + cond_resched(); > continue; > } > > @@ -1079,6 +1080,7 @@ static int rcu_gp_kthread(void *arg) > */ > rsp->fqs_need_gp = 1; > raw_spin_unlock_irqrestore(&rnp->lock, flags); > + cond_resched(); > continue; > } > > @@ -1089,10 +1091,10 @@ static int rcu_gp_kthread(void *arg) > rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ > rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; > record_gp_stall_check_time(rsp); > - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > /* Exclude any concurrent CPU-hotplug operations. */ > - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ > + get_online_cpus(); > > /* > * Set the quiescent-state-needed bits in all the rcu_node > @@ -1112,7 +1114,7 @@ static int rcu_gp_kthread(void *arg) > * due to the fact that we have irqs disabled. > */ > rcu_for_each_node_breadth_first(rsp, rnp) { > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > + raw_spin_lock_irqsave(&rnp->lock, flags); > rcu_preempt_check_blocked_tasks(rnp); > rnp->qsmask = rnp->qsmaskinit; > rnp->gpnum = rsp->gpnum; > @@ -1123,15 +1125,16 @@ static int rcu_gp_kthread(void *arg) > trace_rcu_grace_period_init(rsp->name, rnp->gpnum, > rnp->level, rnp->grplo, > rnp->grphi, rnp->qsmask); > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > + cond_resched(); > } > > rnp = rcu_get_root(rsp); > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > + raw_spin_lock_irqsave(&rnp->lock, flags); > /* force_quiescent_state() now OK. */ > rsp->fqs_state = RCU_SIGNAL_INIT; > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > + put_online_cpus(); > } > return 0; > } > -- > 1.7.8 >
On Sat, Sep 01, 2012 at 06:09:35PM -0700, Josh Triplett wrote: > On Thu, Aug 30, 2012 at 11:18:17AM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > RCU grace-period initialization is currently carried out with interrupts > > disabled, which can result in 200-microsecond latency spikes on systems > > on which RCU has been configured for 4096 CPUs. This patch therefore > > makes the RCU grace-period initialization be preemptible, which should > > eliminate those latency spikes. Similar spikes from grace-period cleanup > > and the forcing of quiescent states will be dealt with similarly by later > > patches. > > > > Reported-by: Mike Galbraith <mgalbraith@suse.de> > > Reported-by: Dimitri Sivanich <sivanich@sgi.com> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > Does it make sense to have cond_resched() right before the continues, > which lead right back up to the wait_event_interruptible at the top of > the loop? Or do you expect to usually find that event already > signalled? Given that the event might have already signaled, I need to put the cond_resched() into the loop. Otherwise, we get back long latencies. Thanx, Paul > In any case: > > Reviewed-by: Josh Triplett <josh@joshtriplett.org> > > > kernel/rcutree.c | 17 ++++++++++------- > > 1 files changed, 10 insertions(+), 7 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index e1c5868..ef56aa3 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1069,6 +1069,7 @@ static int rcu_gp_kthread(void *arg) > > * don't start another one. > > */ > > raw_spin_unlock_irqrestore(&rnp->lock, flags); > > + cond_resched(); > > continue; > > } > > > > @@ -1079,6 +1080,7 @@ static int rcu_gp_kthread(void *arg) > > */ > > rsp->fqs_need_gp = 1; > > raw_spin_unlock_irqrestore(&rnp->lock, flags); > > + cond_resched(); > > continue; > > } > > > > @@ -1089,10 +1091,10 @@ static int rcu_gp_kthread(void *arg) > > rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ > > rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; > > record_gp_stall_check_time(rsp); > > - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > > > /* Exclude any concurrent CPU-hotplug operations. */ > > - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ > > + get_online_cpus(); > > > > /* > > * Set the quiescent-state-needed bits in all the rcu_node > > @@ -1112,7 +1114,7 @@ static int rcu_gp_kthread(void *arg) > > * due to the fact that we have irqs disabled. > > */ > > rcu_for_each_node_breadth_first(rsp, rnp) { > > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > > + raw_spin_lock_irqsave(&rnp->lock, flags); > > rcu_preempt_check_blocked_tasks(rnp); > > rnp->qsmask = rnp->qsmaskinit; > > rnp->gpnum = rsp->gpnum; > > @@ -1123,15 +1125,16 @@ static int rcu_gp_kthread(void *arg) > > trace_rcu_grace_period_init(rsp->name, rnp->gpnum, > > rnp->level, rnp->grplo, > > rnp->grphi, rnp->qsmask); > > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > + cond_resched(); > > } > > > > rnp = rcu_get_root(rsp); > > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > > + raw_spin_lock_irqsave(&rnp->lock, flags); > > /* force_quiescent_state() now OK. */ > > rsp->fqs_state = RCU_SIGNAL_INIT; > > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > > - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); > > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > + put_online_cpus(); > > } > > return 0; > > } > > -- > > 1.7.8 > > >
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e1c5868..ef56aa3 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1069,6 +1069,7 @@ static int rcu_gp_kthread(void *arg) * don't start another one. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); + cond_resched(); continue; } @@ -1079,6 +1080,7 @@ static int rcu_gp_kthread(void *arg) */ rsp->fqs_need_gp = 1; raw_spin_unlock_irqrestore(&rnp->lock, flags); + cond_resched(); continue; } @@ -1089,10 +1091,10 @@ static int rcu_gp_kthread(void *arg) rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); /* Exclude any concurrent CPU-hotplug operations. */ - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ + get_online_cpus(); /* * Set the quiescent-state-needed bits in all the rcu_node @@ -1112,7 +1114,7 @@ static int rcu_gp_kthread(void *arg) * due to the fact that we have irqs disabled. */ rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irqsave(&rnp->lock, flags); rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; @@ -1123,15 +1125,16 @@ static int rcu_gp_kthread(void *arg) trace_rcu_grace_period_init(rsp->name, rnp->gpnum, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); + cond_resched(); } rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irqsave(&rnp->lock, flags); /* force_quiescent_state() now OK. */ rsp->fqs_state = RCU_SIGNAL_INIT; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + raw_spin_unlock_irqrestore(&rnp->lock, flags); + put_online_cpus(); } return 0; }