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rcu: Add accessor macros for the ->need_future_gp[] array

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Accessors for the ->need_future_gp[] array are currently open-coded,
which makes them difficult to change.  To improve maintainability, this
commit adds need_future_gp_mask() to compute the indexing mask from the
array size, need_future_gp_element() to access the element corresponding
to the specified grace-period number, and need_any_future_gp() to
determine if any future grace period is needed.  This commit also applies
need_future_gp_element() to existing open-coded single-element accesses.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>
This commit is contained in:
Paul E. McKenney 2018-04-18 11:11:39 -07:00
parent 825a9911f6
commit c91a8675b9
3 changed files with 23 additions and 10 deletions
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16
kernel/rcu/tree.c
View file

@ -718,11 +718,9 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
static int rcu_future_needs_gp(struct rcu_state *rsp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
int *fp = &rnp->need_future_gp[idx];
lockdep_assert_irqs_disabled();
return READ_ONCE(*fp);
return READ_ONCE(need_future_gp_element(rnp, rnp->completed));
}
/*
@ -1699,7 +1697,7 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
*/
c = rcu_cbs_completed(rdp->rsp, rnp);
trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
if (rnp->need_future_gp[c & 0x1]) {
if (need_future_gp_element(rnp, c)) {
trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
goto out;
}
@ -1711,7 +1709,7 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
* current grace period, we don't need to explicitly start one.
*/
if (rnp->gpnum != rnp->completed) {
rnp->need_future_gp[c & 0x1]++;
need_future_gp_element(rnp, c)++;
trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
goto out;
}
@ -1737,13 +1735,13 @@ rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
* If the needed for the required grace period is already
* recorded, trace and leave.
*/
if (rnp_root->need_future_gp[c & 0x1]) {
if (need_future_gp_element(rnp_root, c)) {
trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
goto unlock_out;
}
/* Record the need for the future grace period. */
rnp_root->need_future_gp[c & 0x1]++;
need_future_gp_element(rnp_root, c)++;
/* If a grace period is not already in progress, start one. */
if (rnp_root->gpnum != rnp_root->completed) {
@ -1771,8 +1769,8 @@ static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
int needmore;
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
rnp->need_future_gp[c & 0x1] = 0;
needmore = rnp->need_future_gp[(c + 1) & 0x1];
need_future_gp_element(rnp, c) = 0;
needmore = need_future_gp_element(rnp, c + 1);
trace_rcu_future_gp(rnp, rdp, c,
needmore ? TPS("CleanupMore") : TPS("Cleanup"));
return needmore;

15
kernel/rcu/tree.h
View file

@ -159,6 +159,21 @@ struct rcu_node {
wait_queue_head_t exp_wq[4];
} ____cacheline_internodealigned_in_smp;
/* Accessors for ->need_future_gp[] array. */
#define need_future_gp_mask() \
(ARRAY_SIZE(((struct rcu_node *)NULL)->need_future_gp) - 1)
#define need_future_gp_element(rnp, c) \
((rnp)->need_future_gp[(c) & need_future_gp_mask()])
#define need_any_future_gp(rnp) \
({ \
int __i; \
bool __nonzero = false; \
\
for (__i = 0; __i < ARRAY_SIZE((rnp)->need_future_gp); __i++) \
__nonzero = __nonzero || (rnp)->need_future_gp[__i]; \
__nonzero; \
})
/*
* Bitmasks in an rcu_node cover the interval [grplo, grphi] of CPU IDs, and
* are indexed relative to this interval rather than the global CPU ID space.

2
kernel/rcu/tree_plugin.h
View file

@ -1790,7 +1790,7 @@ static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
*/
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
{
rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
need_future_gp_element(rnp, rnp->completed + 1) += nrq;
}
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)