| Message ID | 1346350718-30937-22-git-send-email-paulmck@linux.vnet.ibm.com |
|---|---|
| State | Superseded |
| Headers | show |
On Thu, Aug 30, 2012 at 11:18:37AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > The synchronize_rcu_expedited() function disables interrupts across a > scan of all leaf rcu_node structures, which is not good for real-time > scheduling latency on large systems (hundreds or especially thousands > of CPUs). This commit therefore holds off CPU-hotplug operations using > get_online_cpus(), and removes the prior acquisiion of the ->onofflock > (which required disabling interrupts). > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org> > kernel/rcutree_plugin.h | 30 ++++++++++++++++++++++-------- > 1 files changed, 22 insertions(+), 8 deletions(-) > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 7ed45c9..f1e06f6 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -800,33 +800,47 @@ void synchronize_rcu_expedited(void) > smp_mb(); /* Above access cannot bleed into critical section. */ > > /* > + * Block CPU-hotplug operations. This means that any CPU-hotplug > + * operation that finds an rcu_node structure with tasks in the > + * process of being boosted will know that all tasks blocking > + * this expedited grace period will already be in the process of > + * being boosted. This simplifies the process of moving tasks > + * from leaf to root rcu_node structures. > + */ > + get_online_cpus(); > + > + /* > * Acquire lock, falling back to synchronize_rcu() if too many > * lock-acquisition failures. Of course, if someone does the > * expedited grace period for us, just leave. > */ > while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { > + if (ULONG_CMP_LT(snap, > + ACCESS_ONCE(sync_rcu_preempt_exp_count))) { > + put_online_cpus(); > + goto mb_ret; /* Others did our work for us. */ > + } > if (trycount++ < 10) { > udelay(trycount * num_online_cpus()); > } else { > + put_online_cpus(); > synchronize_rcu(); > return; > } > - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) > - goto mb_ret; /* Others did our work for us. */ > } > - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) > + if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { > + put_online_cpus(); > goto unlock_mb_ret; /* Others did our work for us. */ > + } > > /* force all RCU readers onto ->blkd_tasks lists. */ > synchronize_sched_expedited(); > > - raw_spin_lock_irqsave(&rsp->onofflock, flags); > - > /* Initialize ->expmask for all non-leaf rcu_node structures. */ > rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { > - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ > + raw_spin_lock_irqsave(&rnp->lock, flags); > rnp->expmask = rnp->qsmaskinit; > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > } > > /* Snapshot current state of ->blkd_tasks lists. */ > @@ -835,7 +849,7 @@ void synchronize_rcu_expedited(void) > if (NUM_RCU_NODES > 1) > sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); > > - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); > + put_online_cpus(); > > /* Wait for snapshotted ->blkd_tasks lists to drain. */ > rnp = rcu_get_root(rsp); > -- > 1.7.8 >
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7ed45c9..f1e06f6 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -800,33 +800,47 @@ void synchronize_rcu_expedited(void) smp_mb(); /* Above access cannot bleed into critical section. */ /* + * Block CPU-hotplug operations. This means that any CPU-hotplug + * operation that finds an rcu_node structure with tasks in the + * process of being boosted will know that all tasks blocking + * this expedited grace period will already be in the process of + * being boosted. This simplifies the process of moving tasks + * from leaf to root rcu_node structures. + */ + get_online_cpus(); + + /* * Acquire lock, falling back to synchronize_rcu() if too many * lock-acquisition failures. Of course, if someone does the * expedited grace period for us, just leave. */ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { + if (ULONG_CMP_LT(snap, + ACCESS_ONCE(sync_rcu_preempt_exp_count))) { + put_online_cpus(); + goto mb_ret; /* Others did our work for us. */ + } if (trycount++ < 10) { udelay(trycount * num_online_cpus()); } else { + put_online_cpus(); synchronize_rcu(); return; } - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) - goto mb_ret; /* Others did our work for us. */ } - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) + if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { + put_online_cpus(); goto unlock_mb_ret; /* Others did our work for us. */ + } /* force all RCU readers onto ->blkd_tasks lists. */ synchronize_sched_expedited(); - raw_spin_lock_irqsave(&rsp->onofflock, flags); - /* Initialize ->expmask for all non-leaf rcu_node structures. */ rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irqsave(&rnp->lock, flags); rnp->expmask = rnp->qsmaskinit; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* Snapshot current state of ->blkd_tasks lists. */ @@ -835,7 +849,7 @@ void synchronize_rcu_expedited(void) if (NUM_RCU_NODES > 1) sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + put_online_cpus(); /* Wait for snapshotted ->blkd_tasks lists to drain. */ rnp = rcu_get_root(rsp);