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rcu: Introduce proper blocking to no-CBs kthreads GP waits

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Currently, the no-CBs kthreads do repeated timed waits for grace periods
to elapse.  This is crude and energy inefficient, so this commit allows
no-CBs kthreads to specify exactly which grace period they are waiting
for and also allows them to block for the entire duration until the
desired grace period completes.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2013-02-10 20:48:58 -08:00 committed by Paul E. McKenney
parent 911af505ef
commit dae6e64d2b
3 changed files with 127 additions and 20 deletions
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6
kernel/rcutree.c
View File

@ -310,7 +310,7 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
if (rcu_gp_in_progress(rsp))
return 0; /* No, a grace period is already in progress. */
if (rcu_nocb_needs_gp(rdp))
if (rcu_nocb_needs_gp(rsp))
return 1; /* Yes, a no-CBs CPU needs one. */
if (!rdp->nxttail[RCU_NEXT_TAIL])
return 0; /* No, this is a no-CBs (or offline) CPU. */
@ -1364,6 +1364,7 @@ int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
static void rcu_gp_cleanup(struct rcu_state *rsp)
{
unsigned long gp_duration;
int nocb = 0;
struct rcu_data *rdp;
struct rcu_node *rnp = rcu_get_root(rsp);
@ -1394,11 +1395,13 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
rcu_for_each_node_breadth_first(rsp, rnp) {
raw_spin_lock_irq(&rnp->lock);
rnp->completed = rsp->gpnum;
nocb += rcu_nocb_gp_cleanup(rsp, rnp);
raw_spin_unlock_irq(&rnp->lock);
cond_resched();
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irq(&rnp->lock);
rcu_nocb_gp_set(rnp, nocb);
rsp->completed = rsp->gpnum; /* Declare grace period done. */
trace_rcu_grace_period(rsp->name, rsp->completed, "end");
@ -3084,6 +3087,7 @@ static void __init rcu_init_one(struct rcu_state *rsp,
}
rnp->level = i;
INIT_LIST_HEAD(&rnp->blkd_tasks);
rcu_init_one_nocb(rnp);
}
}

12
kernel/rcutree.h
View File

@ -196,6 +196,12 @@ struct rcu_node {
/* Refused to boost: not sure why, though. */
/* This can happen due to race conditions. */
#endif /* #ifdef CONFIG_RCU_BOOST */
#ifdef CONFIG_RCU_NOCB_CPU
wait_queue_head_t nocb_gp_wq[2];
/* Place for rcu_nocb_kthread() to wait GP. */
int n_nocb_gp_requests[2];
/* Counts of upcoming no-CB GP requests. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp;
} ____cacheline_internodealigned_in_smp;
@ -326,7 +332,6 @@ struct rcu_data {
int nocb_p_count_lazy; /* (approximate). */
wait_queue_head_t nocb_wq; /* For nocb kthreads to sleep on. */
struct task_struct *nocb_kthread;
bool nocb_needs_gp;
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
int cpu;
@ -524,7 +529,10 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static void increment_cpu_stall_ticks(void);
static int rcu_nocb_needs_gp(struct rcu_data *rdp);
static int rcu_nocb_needs_gp(struct rcu_state *rsp);
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);
static void rcu_init_one_nocb(struct rcu_node *rnp);
static bool is_nocb_cpu(int cpu);
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
bool lazy);

129
kernel/rcutree_plugin.h
View File

@ -2176,11 +2176,51 @@ static int __init parse_rcu_nocb_poll(char *arg)
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
/*
* Does this CPU needs a grace period due to offloaded callbacks?
* Do any no-CBs CPUs need another grace period?
*
* Interrupts must be disabled. If the caller does not hold the root
* rnp_node structure's ->lock, the results are advisory only.
*/
static int rcu_nocb_needs_gp(struct rcu_data *rdp)
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
{
return rdp->nocb_needs_gp;
struct rcu_node *rnp = rcu_get_root(rsp);
return rnp->n_nocb_gp_requests[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
}
/*
* Clean up this rcu_node structure's no-CBs state at the end of
* a grace period, and also return whether any no-CBs CPU associated
* with this rcu_node structure needs another grace period.
*/
static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
int c = rnp->completed;
int needmore;
wake_up_all(&rnp->nocb_gp_wq[c & 0x1]);
rnp->n_nocb_gp_requests[c & 0x1] = 0;
needmore = rnp->n_nocb_gp_requests[(c + 1) & 0x1];
return needmore;
}
/*
* Set the root rcu_node structure's ->n_nocb_gp_requests field
* based on the sum of those of all rcu_node structures. This does
* double-count the root rcu_node structure's requests, but this
* is necessary to handle the possibility of a rcu_nocb_kthread()
* having awakened during the time that the rcu_node structures
* were being updated for the end of the previous grace period.
*/
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
rnp->n_nocb_gp_requests[(rnp->completed + 1) & 0x1] += nrq;
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
init_waitqueue_head(&rnp->nocb_gp_wq[0]);
init_waitqueue_head(&rnp->nocb_gp_wq[1]);
}
/* Is the specified CPU a no-CPUs CPU? */
@ -2289,31 +2329,73 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
{
unsigned long c;
bool d;
unsigned long flags;
unsigned long j;
unsigned long flags1;
struct rcu_node *rnp = rdp->mynode;
struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
c = rnp->completed + 2;
rdp->nocb_needs_gp = true;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
/* Count our request for a grace period. */
rnp->n_nocb_gp_requests[c & 0x1]++;
if (rnp->gpnum != rnp->completed) {
/*
* This rcu_node structure believes that a grace period
* is in progress, so we are done. When this grace
* period ends, our request will be acted upon.
*/
raw_spin_unlock_irqrestore(&rnp->lock, flags);
} else {
/*
* Might not be a grace period, check root rcu_node
* structure to see if we must start one.
*/
if (rnp != rnp_root)
raw_spin_lock(&rnp_root->lock); /* irqs disabled. */
if (rnp_root->gpnum != rnp_root->completed) {
raw_spin_unlock(&rnp_root->lock); /* irqs disabled. */
} else {
/*
* No grace period, so we need to start one.
* The good news is that we can wait for exactly
* one grace period instead of part of the current
* grace period and all of the next grace period.
* Adjust counters accordingly and start the
* needed grace period.
*/
rnp->n_nocb_gp_requests[c & 0x1]--;
c = rnp_root->completed + 1;
rnp->n_nocb_gp_requests[c & 0x1]++;
rnp_root->n_nocb_gp_requests[c & 0x1]++;
local_save_flags(flags1);
rcu_start_gp(rdp->rsp, flags1); /* Rlses ->lock. */
}
/* Clean up locking and irq state. */
if (rnp != rnp_root)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
else
local_irq_restore(flags);
}
/*
* Wait for the grace period. Do so interruptibly to avoid messing
* up the load average.
*/
for (;;) {
j = jiffies;
schedule_timeout_interruptible(2);
raw_spin_lock_irqsave(&rnp->lock, flags);
if (ULONG_CMP_GE(rnp->completed, c)) {
rdp->nocb_needs_gp = false;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
wait_event_interruptible(
rnp->nocb_gp_wq[c & 0x1],
(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
if (likely(d))
break;
}
if (j == jiffies)
flush_signals(current);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
flush_signals(current);
}
smp_mb(); /* Ensure that CB invocation happens after GP end. */
}
@ -2416,11 +2498,24 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static int rcu_nocb_needs_gp(struct rcu_data *rdp)
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
{
return 0;
}
static int rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
return 0;
}
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
}
static void rcu_init_one_nocb(struct rcu_node *rnp)
{
}
static bool is_nocb_cpu(int cpu)
{
return false;