Commit-ID: c1935209df8c903fc3a33143223338826fa54bd1
Gitweb: https://git.kernel.org/tip/c1935209df8c903fc3a33143223338826fa54bd1
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 12 Apr 2018 16:29:13 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 15 May 2018 10:30:59 -0700
rcu: Simplify and inline cpu_needs_another_gp()
Now that RCU no longer relies on failsafe checks, cpu_needs_another_gp()
can be greatly simplified. This simplification eliminates the last
call to rcu_future_needs_gp() and to rcu_segcblist_future_gp_needed(),
both of which which can then be eliminated. And then, because
cpu_needs_another_gp() is called only from __rcu_pending(), it can be
inlined and eliminated.
This commit carries out the simplification, inlining, and elimination
called out above.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
kernel/rcu/rcu_segcblist.c | 18 ------------------
kernel/rcu/rcu_segcblist.h | 2 --
kernel/rcu/tree.c | 40 +++-------------------------------------
3 files changed, 3 insertions(+), 57 deletions(-)
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index 88cba7c2956c..5aff271adf1e 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -403,24 +403,6 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq)
return true;
}
-/*
- * Scan the specified rcu_segcblist structure for callbacks that need
- * a grace period later than the one specified by "seq". We don't look
- * at the RCU_DONE_TAIL or RCU_NEXT_TAIL segments because they don't
- * have a grace-period sequence number.
- */
-bool rcu_segcblist_future_gp_needed(struct rcu_segcblist *rsclp,
- unsigned long seq)
-{
- int i;
-
- for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
- if (rsclp->tails[i - 1] != rsclp->tails[i] &&
- ULONG_CMP_LT(seq, rsclp->gp_seq[i]))
- return true;
- return false;
-}
-
/*
* Merge the source rcu_segcblist structure into the destination
* rcu_segcblist structure, then initialize the source. Any pending
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 581c12b63544..948470cef385 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -134,7 +134,5 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
struct rcu_cblist *rclp);
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 7776d709e060..020a0fe2dbee 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -708,42 +708,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
return &rsp->node[0];
}
-/*
- * Is there any need for future grace periods?
- * Interrupts must be disabled. If the caller does not hold the root
- * rnp_node structure's ->lock, the results are advisory only.
- */
-static int rcu_future_needs_gp(struct rcu_state *rsp)
-{
- struct rcu_node *rnp = rcu_get_root(rsp);
-
- lockdep_assert_irqs_disabled();
- return need_any_future_gp(rnp);
-}
-
-/*
- * Does the current CPU require a not-yet-started grace period?
- * The caller must have disabled interrupts to prevent races with
- * normal callback registry.
- */
-static bool
-cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
-{
- lockdep_assert_irqs_disabled();
- if (rcu_gp_in_progress(rsp))
- return false; /* No, a grace period is already in progress. */
- if (rcu_future_needs_gp(rsp))
- return true; /* Yes, a no-CBs CPU needs one. */
- if (!rcu_segcblist_is_enabled(&rdp->cblist))
- return false; /* No, this is a no-CBs (or offline) CPU. */
- if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
- return true; /* Yes, CPU has newly registered callbacks. */
- if (rcu_segcblist_future_gp_needed(&rdp->cblist,
- READ_ONCE(rsp->completed)))
- return true; /* Yes, CBs for future grace period. */
- return false; /* No grace period needed. */
-}
-
/*
* Enter an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution.
@@ -3298,7 +3262,9 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
return 1;
/* Has RCU gone idle with this CPU needing another grace period? */
- if (cpu_needs_another_gp(rsp, rdp))
+ if (!rcu_gp_in_progress(rsp) &&
+ rcu_segcblist_is_enabled(&rdp->cblist) &&
+ !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
return 1;
/* Has another RCU grace period completed? */
--
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