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Date: Sat, 1 Sep 2012 19:11:22 -0700
From: Josh Triplett <josh@...htriplett.org>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
dipankar@...ibm.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
fweisbec@...il.com, sbw@....edu, patches@...aro.org
Subject: Re: [PATCH tip/core/rcu 06/23] rcu: Break up rcu_gp_kthread() into
subfunctions
On Thu, Aug 30, 2012 at 11:18:21AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>
> Then rcu_gp_kthread() function is too large and furthermore needs to
> have the force_quiescent_state() code pulled in. This commit therefore
> breaks up rcu_gp_kthread() into rcu_gp_init() and rcu_gp_cleanup().
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@...htriplett.org>
> kernel/rcutree.c | 260 +++++++++++++++++++++++++++++-------------------------
> 1 files changed, 138 insertions(+), 122 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 84a6f55..c2c036f 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1040,160 +1040,176 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
> }
>
> /*
> - * Body of kthread that handles grace periods.
> + * Initialize a new grace period.
> */
> -static int rcu_gp_kthread(void *arg)
> +static int rcu_gp_init(struct rcu_state *rsp)
> {
> unsigned long flags;
> - unsigned long gp_duration;
> struct rcu_data *rdp;
> - struct rcu_node *rnp;
> - struct rcu_state *rsp = arg;
> + struct rcu_node *rnp = rcu_get_root(rsp);
>
> - for (;;) {
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> + rsp->gp_flags = 0;
>
> - /* Handle grace-period start. */
> - rnp = rcu_get_root(rsp);
> - for (;;) {
> - wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
> - if (rsp->gp_flags)
> - break;
> - flush_signals(current);
> - }
> + if (rcu_gp_in_progress(rsp)) {
> + /* Grace period already in progress, don't start another. */
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + return 0;
> + }
> +
> + if (rsp->fqs_active) {
> + /*
> + * We need a grace period, but force_quiescent_state()
> + * is running. Tell it to start one on our behalf.
> + */
> + rsp->fqs_need_gp = 1;
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + return 0;
> + }
> +
> + /* Advance to a new grace period and initialize state. */
> + rsp->gpnum++;
> + trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
> + WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
> + 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_irqrestore(&rnp->lock, flags);
> +
> + /* Exclude any concurrent CPU-hotplug operations. */
> + get_online_cpus();
> +
> + /*
> + * Set the quiescent-state-needed bits in all the rcu_node
> + * structures for all currently online CPUs in breadth-first order,
> + * starting from the root rcu_node structure, relying on the layout
> + * of the tree within the rsp->node[] array. Note that other CPUs
> + * access only the leaves of the hierarchy, thus seeing that no
> + * grace period is in progress, at least until the corresponding
> + * leaf node has been initialized. In addition, we have excluded
> + * CPU-hotplug operations.
> + *
> + * The grace period cannot complete until the initialization
> + * process finishes, because this kthread handles both.
> + */
> + rcu_for_each_node_breadth_first(rsp, rnp) {
> raw_spin_lock_irqsave(&rnp->lock, flags);
> - rsp->gp_flags = 0;
> rdp = this_cpu_ptr(rsp->rda);
> + rcu_preempt_check_blocked_tasks(rnp);
> + rnp->qsmask = rnp->qsmaskinit;
> + rnp->gpnum = rsp->gpnum;
> + rnp->completed = rsp->completed;
> + if (rnp == rdp->mynode)
> + rcu_start_gp_per_cpu(rsp, rnp, rdp);
> + rcu_preempt_boost_start_gp(rnp);
> + trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
> + rnp->level, rnp->grplo,
> + rnp->grphi, rnp->qsmask);
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + cond_resched();
> + }
>
> - if (rcu_gp_in_progress(rsp)) {
> - /*
> - * A grace period is already in progress, so
> - * don't start another one.
> - */
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - cond_resched();
> - continue;
> - }
> + rnp = rcu_get_root(rsp);
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> + /* force_quiescent_state() now OK. */
> + rsp->fqs_state = RCU_SIGNAL_INIT;
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + put_online_cpus();
>
> - if (rsp->fqs_active) {
> - /*
> - * We need a grace period, but force_quiescent_state()
> - * is running. Tell it to start one on our behalf.
> - */
> - rsp->fqs_need_gp = 1;
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - cond_resched();
> - continue;
> - }
> + return 1;
> +}
>
> - /* Advance to a new grace period and initialize state. */
> - rsp->gpnum++;
> - trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
> - WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT);
> - 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_irqrestore(&rnp->lock, flags);
> +/*
> + * Clean up after the old grace period.
> + */
> +static int rcu_gp_cleanup(struct rcu_state *rsp)
> +{
> + unsigned long flags;
> + unsigned long gp_duration;
> + struct rcu_data *rdp;
> + struct rcu_node *rnp = rcu_get_root(rsp);
>
> - /* Exclude any concurrent CPU-hotplug operations. */
> - get_online_cpus();
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> + gp_duration = jiffies - rsp->gp_start;
> + if (gp_duration > rsp->gp_max)
> + rsp->gp_max = gp_duration;
> +
> + /*
> + * We know the grace period is complete, but to everyone else
> + * it appears to still be ongoing. But it is also the case
> + * that to everyone else it looks like there is nothing that
> + * they can do to advance the grace period. It is therefore
> + * safe for us to drop the lock in order to mark the grace
> + * period as completed in all of the rcu_node structures.
> + *
> + * But if this CPU needs another grace period, it will take
> + * care of this while initializing the next grace period.
> + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
> + * because the callbacks have not yet been advanced: Those
> + * callbacks are waiting on the grace period that just now
> + * completed.
> + */
> + rdp = this_cpu_ptr(rsp->rda);
> + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
>
> /*
> - * Set the quiescent-state-needed bits in all the rcu_node
> - * structures for all currently online CPUs in breadth-first
> - * order, starting from the root rcu_node structure.
> - * This operation relies on the layout of the hierarchy
> - * within the rsp->node[] array. Note that other CPUs will
> - * access only the leaves of the hierarchy, which still
> - * indicate that no grace period is in progress, at least
> - * until the corresponding leaf node has been initialized.
> - * In addition, we have excluded CPU-hotplug operations.
> - *
> - * Note that the grace period cannot complete until
> - * we finish the initialization process, as there will
> - * be at least one qsmask bit set in the root node until
> - * that time, namely the one corresponding to this CPU,
> - * due to the fact that we have irqs 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.
> */
> rcu_for_each_node_breadth_first(rsp, rnp) {
> raw_spin_lock_irqsave(&rnp->lock, flags);
> - rcu_preempt_check_blocked_tasks(rnp);
> - rnp->qsmask = rnp->qsmaskinit;
> - rnp->gpnum = rsp->gpnum;
> - rnp->completed = rsp->completed;
> - if (rnp == rdp->mynode)
> - rcu_start_gp_per_cpu(rsp, rnp, rdp);
> - rcu_preempt_boost_start_gp(rnp);
> - trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
> - rnp->level, rnp->grplo,
> - rnp->grphi, rnp->qsmask);
> + rnp->completed = rsp->gpnum;
> raw_spin_unlock_irqrestore(&rnp->lock, flags);
> cond_resched();
> }
> -
> rnp = rcu_get_root(rsp);
> raw_spin_lock_irqsave(&rnp->lock, flags);
> - /* force_quiescent_state() now OK. */
> - rsp->fqs_state = RCU_SIGNAL_INIT;
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - put_online_cpus();
> + }
> +
> + rsp->completed = rsp->gpnum; /* Declare grace period done. */
> + trace_rcu_grace_period(rsp->name, rsp->completed, "end");
> + rsp->fqs_state = RCU_GP_IDLE;
> + rdp = this_cpu_ptr(rsp->rda);
> + if (cpu_needs_another_gp(rsp, rdp))
> + rsp->gp_flags = 1;
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> + return 1;
> +}
> +
> +/*
> + * Body of kthread that handles grace periods.
> + */
> +static int rcu_gp_kthread(void *arg)
> +{
> + struct rcu_state *rsp = arg;
> + struct rcu_node *rnp = rcu_get_root(rsp);
> +
> + for (;;) {
> +
> + /* Handle grace-period start. */
> + for (;;) {
> + wait_event_interruptible(rsp->gp_wq, rsp->gp_flags);
> + if (rsp->gp_flags && rcu_gp_init(rsp))
> + break;
> + cond_resched();
> + flush_signals(current);
> + }
>
> /* Handle grace-period end. */
> - rnp = rcu_get_root(rsp);
> for (;;) {
> wait_event_interruptible(rsp->gp_wq,
> !ACCESS_ONCE(rnp->qsmask) &&
> !rcu_preempt_blocked_readers_cgp(rnp));
> if (!ACCESS_ONCE(rnp->qsmask) &&
> - !rcu_preempt_blocked_readers_cgp(rnp))
> + !rcu_preempt_blocked_readers_cgp(rnp) &&
> + rcu_gp_cleanup(rsp))
> break;
> + cond_resched();
> flush_signals(current);
> }
> -
> - raw_spin_lock_irqsave(&rnp->lock, flags);
> - gp_duration = jiffies - rsp->gp_start;
> - if (gp_duration > rsp->gp_max)
> - rsp->gp_max = gp_duration;
> -
> - /*
> - * We know the grace period is complete, but to everyone else
> - * it appears to still be ongoing. But it is also the case
> - * that to everyone else it looks like there is nothing that
> - * they can do to advance the grace period. It is therefore
> - * safe for us to drop the lock in order to mark the grace
> - * period as completed in all of the rcu_node structures.
> - *
> - * But if this CPU needs another grace period, it will take
> - * care of this while initializing the next grace period.
> - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
> - * because the callbacks have not yet been advanced: Those
> - * callbacks are waiting on the grace period that just now
> - * completed.
> - */
> - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> -
> - /*
> - * 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.
> - */
> - rcu_for_each_node_breadth_first(rsp, rnp) {
> - raw_spin_lock_irqsave(&rnp->lock, flags);
> - rnp->completed = rsp->gpnum;
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> - cond_resched();
> - }
> - rnp = rcu_get_root(rsp);
> - raw_spin_lock_irqsave(&rnp->lock, flags);
> - }
> -
> - rsp->completed = rsp->gpnum; /* Declare grace period done. */
> - trace_rcu_grace_period(rsp->name, rsp->completed, "end");
> - rsp->fqs_state = RCU_GP_IDLE;
> - if (cpu_needs_another_gp(rsp, rdp))
> - rsp->gp_flags = 1;
> - raw_spin_unlock_irqrestore(&rnp->lock, flags);
> }
> return 0;
> }
> --
> 1.7.8
>
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