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rcu/nocb: Use separate flag to indicate offloaded ->cblist 

RCU callback processing currently uses rcu_is_nocb_cpu() to determine
whether or not the current CPU's callbacks are to be offloaded.
This works, but it is not so good for cache locality.  Plus use of
->cblist for offloaded callbacks will greatly increase the frequency
of these checks.  This commit therefore adds a ->offloaded flag to the
rcu_segcblist structure to provide a more flexible and cache-friendly
means of checking for callback offloading.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-04-12 15:58:34 -07:00
parent 1bb5f9b95a
commit ce5215c134
5 changed files with 33 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/rcu_segcblist.h
View File

@ -71,6 +71,7 @@ struct rcu_segcblist {
long len;
long len_lazy;
u8 enabled;
u8 offloaded;
};
#define RCU_SEGCBLIST_INITIALIZER(n) \

12
kernel/rcu/rcu_segcblist.c
View File

@ -73,6 +73,18 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
rsclp->enabled = 0;
}
/*
* Mark the specified rcu_segcblist structure as offloaded. This
* structure must be empty.
*/
void rcu_segcblist_offload(struct rcu_segcblist *rsclp)
{
WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
rsclp->offloaded = 1;
}
/*
* Does the specified rcu_segcblist structure contain callbacks that
* are ready to be invoked?

7
kernel/rcu/rcu_segcblist.h
View File

@ -66,6 +66,12 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
return rsclp->enabled;
}
/* Is the specified rcu_segcblist offloaded? */
static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
{
return rsclp->offloaded;
}
/*
* Are all segments following the specified segment of the specified
* rcu_segcblist structure empty of callbacks? (The specified
@ -78,6 +84,7 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
void rcu_segcblist_init(struct rcu_segcblist *rsclp);
void rcu_segcblist_disable(struct rcu_segcblist *rsclp);
void rcu_segcblist_offload(struct rcu_segcblist *rsclp);
bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp);
bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp);
struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);

10
kernel/rcu/tree.c
View File

@ -2858,10 +2858,11 @@ void rcu_barrier(void)
* corresponding CPU's preceding callbacks have been invoked.
*/
for_each_possible_cpu(cpu) {
if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
continue;
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_is_nocb_cpu(cpu)) {
if (!cpu_online(cpu) &&
!rcu_segcblist_is_offloaded(&rdp->cblist))
continue;
if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
if (!rcu_nocb_cpu_needs_barrier(cpu)) {
rcu_barrier_trace(TPS("OfflineNoCB"), cpu,
rcu_state.barrier_sequence);
@ -3155,7 +3156,8 @@ void rcutree_migrate_callbacks(int cpu)
struct rcu_node *rnp_root = rcu_get_root();
bool needwake;
if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
if (rcu_segcblist_is_offloaded(&rdp->cblist) ||
rcu_segcblist_empty(&rdp->cblist))
return; /* No callbacks to migrate. */
local_irq_save(flags);

11
kernel/rcu/tree_plugin.h
View File

@ -1382,7 +1382,7 @@ static void rcu_prepare_for_idle(void)
int tne;
lockdep_assert_irqs_disabled();
if (rcu_is_nocb_cpu(smp_processor_id()))
if (rcu_segcblist_is_offloaded(&rdp->cblist))
return;
/* Handle nohz enablement switches conservatively. */
@ -1431,8 +1431,10 @@ static void rcu_prepare_for_idle(void)
*/
static void rcu_cleanup_after_idle(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
lockdep_assert_irqs_disabled();
if (rcu_is_nocb_cpu(smp_processor_id()))
if (rcu_segcblist_is_offloaded(&rdp->cblist))
return;
if (rcu_try_advance_all_cbs())
invoke_rcu_core();
@ -1694,7 +1696,7 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
bool lazy, unsigned long flags)
{
if (!rcu_is_nocb_cpu(rdp->cpu))
if (!rcu_segcblist_is_offloaded(&rdp->cblist))
return false;
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
if (__is_kfree_rcu_offset((unsigned long)rhp->func))
@ -1729,7 +1731,7 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
unsigned long flags)
{
lockdep_assert_irqs_disabled();
if (!rcu_is_nocb_cpu(smp_processor_id()))
if (!rcu_segcblist_is_offloaded(&my_rdp->cblist))
return false; /* Not NOCBs CPU, caller must migrate CBs. */
__call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
rcu_segcblist_tail(&rdp->cblist),
@ -2192,6 +2194,7 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
}
rcu_segcblist_init(&rdp->cblist);
rcu_segcblist_disable(&rdp->cblist);
rcu_segcblist_offload(&rdp->cblist);
return true;
}