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Date: Mon, 24 Jul 2017 14:51:54 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: 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,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 10/12] rcu: Localize rcu_state ->orphan_pend and ->orphan_done
Given that the rcu_state structure's >orphan_pend and ->orphan_done
fields are used only during migration of callbacks from the recently
offlined CPU to a surviving CPU, if rcu_send_cbs_to_orphanage() and
rcu_adopt_orphan_cbs() are combined, these fields can become local
variables in the combined function. This commit therefore combines
rcu_send_cbs_to_orphanage() and rcu_adopt_orphan_cbs() into a new
rcu_segcblist_merge() function and removes the ->orphan_pend and
->orphan_done fields.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/rcu_segcblist.c | 24 +++++++++++++++
kernel/rcu/rcu_segcblist.h | 2 ++
kernel/rcu/tree.c | 73 +++-------------------------------------------
kernel/rcu/tree.h | 6 ----
4 files changed, 30 insertions(+), 75 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 2b62a38b080f..7091d824b893 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -503,3 +503,27 @@ bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
return true;
return false;
}
+
+/*
+ * Merge the source rcu_segcblist structure into the destination
+ * rcu_segcblist structure, then initialize the source. Any pending
+ * callbacks from the source get to start over. It is best to
+ * advance and accelerate both the destination and the source
+ * before merging.
+ */
+void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,
+ struct rcu_segcblist *src_rsclp)
+{
+ struct rcu_cblist donecbs;
+ struct rcu_cblist pendcbs;
+
+ rcu_cblist_init(&donecbs);
+ rcu_cblist_init(&pendcbs);
+ rcu_segcblist_extract_count(src_rsclp, &donecbs);
+ rcu_segcblist_extract_done_cbs(src_rsclp, &donecbs);
+ rcu_segcblist_extract_pend_cbs(src_rsclp, &pendcbs);
+ rcu_segcblist_insert_count(dst_rsclp, &donecbs);
+ rcu_segcblist_insert_done_cbs(dst_rsclp, &donecbs);
+ rcu_segcblist_insert_pend_cbs(dst_rsclp, &pendcbs);
+ rcu_segcblist_init(src_rsclp);
+}
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 6e36e36478cd..c2f319f3f06a 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -162,3 +162,5 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);
bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);
bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
unsigned long seq);
+void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,
+ struct rcu_segcblist *src_rsclp);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f9f01aeb5add..d330c17c8df4 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -97,8 +97,6 @@ struct rcu_state sname##_state = { \
.gp_state = RCU_GP_IDLE, \
.gpnum = 0UL - 300UL, \
.completed = 0UL - 300UL, \
- .orphan_pend = RCU_CBLIST_INITIALIZER(sname##_state.orphan_pend), \
- .orphan_done = RCU_CBLIST_INITIALIZER(sname##_state.orphan_done), \
.barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
.name = RCU_STATE_NAME(sname), \
.abbr = sabbr, \
@@ -3850,76 +3848,12 @@ void rcu_report_dead(unsigned int cpu)
rcu_cleanup_dying_idle_cpu(cpu, rsp);
}
-/*
- * Send the specified CPU's RCU callbacks to the orphanage. The
- * specified CPU must be offline.
- */
-static void
-rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
- struct rcu_node *rnp, struct rcu_data *rdp)
-{
- /*
- * Orphan the callbacks. First adjust the counts. This is safe
- * because _rcu_barrier() excludes CPU-hotplug operations, so it
- * cannot be running now. Thus no memory barrier is required.
- */
- rcu_segcblist_extract_count(&rdp->cblist, &rsp->orphan_done);
-
- /*
- * Next, move those callbacks still needing a grace period to
- * the orphanage, where some other CPU will pick them up.
- * Some of the callbacks might have gone partway through a grace
- * period, but that is too bad. They get to start over because we
- * cannot assume that grace periods are synchronized across CPUs.
- */
- rcu_segcblist_extract_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
-
- /*
- * Then move the ready-to-invoke callbacks to the orphanage,
- * where some other CPU will pick them up. These will not be
- * required to pass though another grace period: They are done.
- */
- rcu_segcblist_extract_done_cbs(&rdp->cblist, &rsp->orphan_done);
-
- /* Finally, disallow further callbacks on this CPU. */
- rcu_segcblist_disable(&rdp->cblist);
-}
-
-/*
- * Adopt the RCU callbacks from the specified rcu_state structure's
- * orphanage.
- */
-static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
-{
- struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
-
- /* Do the accounting first. */
- if (rsp->orphan_done.len_lazy != rsp->orphan_done.len)
- rcu_idle_count_callbacks_posted();
- rcu_segcblist_insert_count(&rdp->cblist, &rsp->orphan_done);
-
- /*
- * We do not need a memory barrier here because the only way we
- * can get here if there is an rcu_barrier() in flight is if
- * we are the task doing the rcu_barrier().
- */
-
- /* First adopt the ready-to-invoke callbacks, then the done ones. */
- rcu_segcblist_insert_done_cbs(&rdp->cblist, &rsp->orphan_done);
- WARN_ON_ONCE(rsp->orphan_done.head);
- rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rsp->orphan_pend);
- WARN_ON_ONCE(rsp->orphan_pend.head);
- WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) !=
- !rcu_segcblist_n_cbs(&rdp->cblist));
-}
-
-/* Orphan the dead CPU's callbacks, and then adopt them. */
+/* Migrate the dead CPU's callbacks to the current CPU. */
static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
{
unsigned long flags;
struct rcu_data *my_rdp;
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
- struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
@@ -3933,15 +3867,16 @@ static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
}
raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */
- rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
- rcu_adopt_orphan_cbs(rsp, flags);
rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */
+ rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
!rcu_segcblist_empty(&rdp->cblist),
"rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
cpu, rcu_segcblist_n_cbs(&rdp->cblist),
rcu_segcblist_first_cb(&rdp->cblist));
+ WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
+ !rcu_segcblist_n_cbs(&my_rdp->cblist));
}
/*
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 62b1d0b0d47c..b99f31c2b0c3 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -348,12 +348,6 @@ struct rcu_state {
/* End of fields guarded by root rcu_node's lock. */
- struct rcu_cblist orphan_pend; /* Orphaned callbacks that */
- /* need a grace period. */
- struct rcu_cblist orphan_done; /* Orphaned callbacks that */
- /* are ready to invoke. */
- /* (Contains counts.) */
-
struct mutex barrier_mutex; /* Guards barrier fields. */
atomic_t barrier_cpu_count; /* # CPUs waiting on. */
struct completion barrier_completion; /* Wake at barrier end. */
--
2.5.2
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