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
parent
755609a908
commit
cabc49c1ff
112
kernel/rcutree.c
112
kernel/rcutree.c
|
|
@ -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. */
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
|
|||
Loading…
Reference in New Issue