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rcu: Move RCU grace-period cleanup into kthread 

As a first step towards allowing grace-period cleanup to be preemptible,
this commit moves the RCU grace-period cleanup into the same kthread
that is now used to initialize grace periods.  This is needed to keep
scheduling latency down to a dull roar.

[ paulmck: Get rid of stray spin_lock_irqsave() calls. ]

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>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2012-06-20 17:07:14 -07:00
parent 755609a908
commit cabc49c1ff
1 changed files with 62 additions and 50 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

112
kernel/rcutree.c
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@ -1032,6 +1032,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
*/
static int __noreturn rcu_gp_kthread(void *arg)
{
unsigned long gp_duration;
struct rcu_data *rdp;
struct rcu_node *rnp;
struct rcu_state *rsp = arg;
@ -1116,6 +1117,65 @@ static int __noreturn rcu_gp_kthread(void *arg)
rsp->fqs_state = RCU_SIGNAL_INIT;
raw_spin_unlock_irq(&rnp->lock);
put_online_cpus();
/* 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))
break;
flush_signals(current);
}
raw_spin_lock_irq(&rnp->lock);
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(&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.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
/* irqs already disabled. */
raw_spin_lock(&rnp->lock);
rnp->completed = rsp->gpnum;
/* irqs remain disabled. */
raw_spin_unlock(&rnp->lock);
}
rnp = rcu_get_root(rsp);
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
}
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_irq(&rnp->lock);
}
}
@ -1162,57 +1222,9 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
__releases(rcu_get_root(rsp)->lock)
{
unsigned long gp_duration;
struct rcu_node *rnp = rcu_get_root(rsp);
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
/*
* Ensure that all grace-period and pre-grace-period activity
* is seen before the assignment to rsp->completed.
*/
smp_mb(); /* See above block comment. */
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(&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.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
rnp->completed = rsp->gpnum;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
rnp = rcu_get_root(rsp);
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
}
rsp->completed = rsp->gpnum; /* Declare the grace period complete. */
trace_rcu_grace_period(rsp->name, rsp->completed, "end");
rsp->fqs_state = RCU_GP_IDLE;
rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
}
/*