Messages in this thread Patch in this message | | | Subject | Re: [PATCH RFC] rcu: Limit GP initialization to CPUs that have been online | From | Mike Galbraith <> | Date | Wed, 14 Mar 2012 10:24:59 +0100 |
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On Tue, 2012-03-13 at 17:24 -0700, Paul E. McKenney wrote: > The following builds, but is only very lightly tested. Probably full > of bug, especially when exercising CPU hotplug.
You didn't say RFT, but...
To beat on this in a rotund 3.0 kernel, the equivalent patch would be the below? My box may well answer that before you can.. hope not ;-)
--- kernel/rcutree.c | 31 ++++++++++++++++++++++++++----- kernel/rcutree.h | 6 ++++-- 2 files changed, 30 insertions(+), 7 deletions(-)
--- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -84,6 +84,8 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_d static struct rcu_state *rcu_state; +int rcu_max_cpu __read_mostly; /* Largest # CPU that has ever been online. */ + /* * The rcu_scheduler_active variable transitions from zero to one just * before the first task is spawned. So when this variable is zero, RCU @@ -827,25 +829,31 @@ rcu_start_gp(struct rcu_state *rsp, unsi struct rcu_node *rnp = rcu_get_root(rsp); if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) { + struct rcu_node *rnp_root = rnp; + if (cpu_needs_another_gp(rsp, rdp)) rsp->fqs_need_gp = 1; - if (rnp->completed == rsp->completed) { - raw_spin_unlock_irqrestore(&rnp->lock, flags); + if (rnp_root->completed == rsp->completed) { + raw_spin_unlock_irqrestore(&rnp_root->lock, flags); return; } - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* * Propagate new ->completed value to rcu_node structures * so that other CPUs don't have to wait until the start * of the next grace period to process their callbacks. + * We must hold the root rcu_node structure's ->lock + * across rcu_for_each_node_breadth_first() in order to + * synchronize with CPUs coming online for the first time. */ rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_unlock(&rnp_root->lock); /* remain disabled. */ raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rnp->completed = rsp->completed; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_lock(&rnp_root->lock); /* already disabled. */ } - local_irq_restore(flags); + raw_spin_unlock_irqrestore(&rnp_root->lock, flags); return; } @@ -935,7 +943,7 @@ static void rcu_report_qs_rsp(struct rcu rsp->gp_max = gp_duration; rsp->completed = rsp->gpnum; rsp->signaled = RCU_GP_IDLE; - rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ + rcu_start_gp(rsp, flags); /* releases root node's ->lock. */ } /* @@ -1862,6 +1870,7 @@ rcu_init_percpu_data(int cpu, struct rcu unsigned long mask; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); + struct rcu_node *rnp_init; /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); @@ -1882,6 +1891,16 @@ rcu_init_percpu_data(int cpu, struct rcu /* Exclude any attempts to start a new GP on large systems. */ raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ + /* Initialize any rcu_node structures that will see their first use. */ + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + for (rnp_init = per_cpu_ptr(rsp->rda, rcu_max_cpu)->mynode + 1; + rnp_init <= rdp->mynode; + rnp_init++) { + rnp_init->gpnum = rsp->gpnum; + rnp_init->completed = rsp->completed; + } + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + /* Add CPU to rcu_node bitmasks. */ rnp = rdp->mynode; mask = rdp->grpmask; @@ -1907,6 +1926,8 @@ static void __cpuinit rcu_prepare_cpu(in rcu_init_percpu_data(cpu, &rcu_sched_state, 0); rcu_init_percpu_data(cpu, &rcu_bh_state, 0); rcu_preempt_init_percpu_data(cpu); + if (cpu > rcu_max_cpu) + rcu_max_cpu = cpu; } /* --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -191,11 +191,13 @@ struct rcu_node { /* * Do a full breadth-first scan of the rcu_node structures for the - * specified rcu_state structure. + * specified rcu_state structure. The caller must hold either the + * ->onofflock or the root rcu_node structure's ->lock. */ +extern int rcu_max_cpu; #define rcu_for_each_node_breadth_first(rsp, rnp) \ for ((rnp) = &(rsp)->node[0]; \ - (rnp) < &(rsp)->node[NUM_RCU_NODES]; (rnp)++) + (rnp) < per_cpu_ptr((rsp)->rda, rcu_max_cpu)->mynode; (rnp)++) /* * Do a breadth-first scan of the non-leaf rcu_node structures for the
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