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rcu: Abstract the dynticks snapshot operation

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This commit is the second step towards full abstraction of all accesses to
the ->dynticks counter, implementing the previously open-coded atomic
add of zero in a new rcu_dynticks_snap() function.  This abstraction will
ease changes o the ->dynticks counter operation.

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 2016-11-02 14:12:05 -07:00
parent 6563de9d6f
commit 8b2f63ab05
2 changed files with 18 additions and 7 deletions
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19
kernel/rcu/tree.c
View file

@ -281,6 +281,17 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
#endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
};
/*
* Snapshot the ->dynticks counter with full ordering so as to allow
* stable comparison of this counter with past and future snapshots.
*/
static int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
{
int snap = atomic_add_return(0, &rdtp->dynticks);
return snap;
}
/*
* Do a double-increment of the ->dynticks counter to emulate a
* momentary idle-CPU quiescent state.
@ -1049,7 +1060,9 @@ void rcu_nmi_exit(void)
*/
bool notrace __rcu_is_watching(void)
{
return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
return atomic_read(&rdtp->dynticks) & 0x1;
}
/**
@ -1132,7 +1145,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
static int dyntick_save_progress_counter(struct rcu_data *rdp,
bool *isidle, unsigned long *maxj)
{
rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
rcu_sysidle_check_cpu(rdp, isidle, maxj);
if ((rdp->dynticks_snap & 0x1) == 0) {
trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
@ -1157,7 +1170,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
int *rcrmp;
unsigned int snap;
curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
curr = (unsigned int)rcu_dynticks_snap(rdp->dynticks);
snap = (unsigned int)rdp->dynticks_snap;
/*

6
kernel/rcu/tree_exp.h
View file

@ -356,10 +356,9 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
mask_ofl_test = 0;
for_each_leaf_node_possible_cpu(rnp, cpu) {
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
rdp->exp_dynticks_snap =
atomic_add_return(0, &rdtp->dynticks);
rcu_dynticks_snap(rdp->dynticks);
if (raw_smp_processor_id() == cpu ||
!(rdp->exp_dynticks_snap & 0x1) ||
!(rnp->qsmaskinitnext & rdp->grpmask))
@ -380,12 +379,11 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
for_each_leaf_node_possible_cpu(rnp, cpu) {
unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
if (!(mask_ofl_ipi & mask))
continue;
retry_ipi:
if (atomic_add_return(0, &rdtp->dynticks) !=
if (rcu_dynticks_snap(rdp->dynticks) !=
rdp->exp_dynticks_snap) {
mask_ofl_test |= mask;
continue;