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Message-Id: <20190801230810.21570-9-paulmck@linux.ibm.com>
Date: Thu, 1 Aug 2019 16:08:01 -0700
From: "Paul E. McKenney" <paulmck@...ux.ibm.com>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org,
jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 09/18] 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@...ux.ibm.com>
---
kernel/rcu/rcu_segcblist.c | 3 ---
kernel/rcu/rcu_segcblist.h | 2 +-
kernel/rcu/tree.c | 5 +++--
kernel/rcu/tree.h | 1 -
kernel/rcu/tree_plugin.h | 35 +++++++----------------------------
5 files changed, 11 insertions(+), 35 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 06435a368be5..9ac28f175627 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -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;
}
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index d9142b3590a8..ed3fcece39a9 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -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)
{
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f1a25d17e3a0..2917ce379b23 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -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();
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index dc3c53cb9608..8d9cfcac6757 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -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);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 9936a66b80bb..2d37fd3fa0d4 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -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;
--
2.17.1
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