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rcu/nocb: Leave ->cblist enabled for no-CBs CPUs 

As a first step towards making no-CBs CPUs use the ->cblist, this commit
leaves the ->cblist enabled for these CPUs.  The main reason to make
no-CBs CPUs use ->cblist is to take advantage of callback numbering,
which will reduce the effects of missed grace periods which in turn will
reduce forward-progress problems for no-CBs CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-05-14 09:50:49 -07:00
parent e6060b41c9
commit e83e73f5b0
5 changed files with 11 additions and 35 deletions
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3
kernel/rcu/rcu_segcblist.c
View File

@ -79,9 +79,6 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
*/
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;
}

2
kernel/rcu/rcu_segcblist.h
View File

@ -59,7 +59,7 @@ static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
/*
* Is the specified rcu_segcblist enabled, for example, not corresponding
* to an offline or callback-offloaded CPU?
* to an offline CPU?
*/
static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
{

5
kernel/rcu/tree.c
View File

@ -2964,7 +2964,8 @@ rcu_boot_init_percpu_data(int cpu)
* Initializes a CPU's per-CPU RCU data. Note that only one online or
* offline event can be happening at a given time. Note also that we can
* accept some slop in the rsp->gp_seq access due to the fact that this
* CPU cannot possibly have any RCU callbacks in flight yet.
* CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
* And any offloaded callbacks are being numbered elsewhere.
*/
int rcutree_prepare_cpu(unsigned int cpu)
{
@ -2978,7 +2979,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
rdp->n_force_qs_snap = rcu_state.n_force_qs;
rdp->blimit = blimit;
if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
!init_nocb_callback_list(rdp))
!rcu_segcblist_is_offloaded(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
rcu_dynticks_eqs_online();

1
kernel/rcu/tree.h
View File

@ -438,7 +438,6 @@ static void __init rcu_spawn_nocb_kthreads(void);
#ifdef CONFIG_RCU_NOCB_CPU
static void __init rcu_organize_nocb_kthreads(void);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
static bool init_nocb_callback_list(struct rcu_data *rdp);
static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp);
static void rcu_bind_gp_kthread(void);
static bool rcu_nohz_full_cpu(void);

35
kernel/rcu/tree_plugin.h
View File

@ -2007,6 +2007,7 @@ void __init rcu_init_nohz(void)
{
int cpu;
bool need_rcu_nocb_mask = false;
struct rcu_data *rdp;
#if defined(CONFIG_NO_HZ_FULL)
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
@ -2040,8 +2041,12 @@ void __init rcu_init_nohz(void)
if (rcu_nocb_poll)
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
for_each_cpu(cpu, rcu_nocb_mask)
init_nocb_callback_list(per_cpu_ptr(&rcu_data, cpu));
for_each_cpu(cpu, rcu_nocb_mask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
rcu_segcblist_offload(&rdp->cblist);
}
rcu_organize_nocb_kthreads();
}
@ -2167,27 +2172,6 @@ static void __init rcu_organize_nocb_kthreads(void)
}
}
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
static bool init_nocb_callback_list(struct rcu_data *rdp)
{
if (!rcu_is_nocb_cpu(rdp->cpu))
return false;
/* If there are early-boot callbacks, move them to nocb lists. */
if (!rcu_segcblist_empty(&rdp->cblist)) {
rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
atomic_long_set(&rdp->nocb_q_count,
rcu_segcblist_n_cbs(&rdp->cblist));
atomic_long_set(&rdp->nocb_q_count_lazy,
rcu_segcblist_n_lazy_cbs(&rdp->cblist));
}
rcu_segcblist_init(&rdp->cblist);
rcu_segcblist_disable(&rdp->cblist);
rcu_segcblist_offload(&rdp->cblist);
return true;
}
/*
* Bind the current task to the offloaded CPUs. If there are no offloaded
* CPUs, leave the task unbound. Splat if the bind attempt fails.
@ -2263,11 +2247,6 @@ static void __init rcu_spawn_nocb_kthreads(void)
{
}
static bool init_nocb_callback_list(struct rcu_data *rdp)
{
return false;
}
static unsigned long rcu_get_n_cbs_nocb_cpu(struct rcu_data *rdp)
{
return 0;