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Date: Mon, 28 Apr 2014 16:56:17 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
oleg@...hat.com, sbw@....edu,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 04/19] rcu: Update cpu_needs_another_gp() for futures from non-NOCB CPUs
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
In the old days, the only source of requests for future grace periods
was NOCB CPUs. This has changed: CPUs routinely post requests for
future grace periods in order to promote power efficiency and reduce
OS jitter with minimal impact on grace-period latency. This commit
therefore updates cpu_needs_another_gp() to invoke rcu_future_needs_gp()
instead of rcu_nocb_needs_gp(). The latter is no longer used, so is
now removed. This commit also adds tracing for the irq_work_queue()
wakeup case.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
kernel/rcu/tree.c | 39 +++++++++++++++++++++++++++++----------
kernel/rcu/tree.h | 1 -
kernel/rcu/tree_plugin.h | 18 ------------------
3 files changed, 29 insertions(+), 29 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b33c29a99df3..b4688993e956 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -324,6 +324,28 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
}
/*
+ * Return the root node of the specified rcu_state structure.
+ */
+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);
+ int idx = (ACCESS_ONCE(rnp->completed) + 1) & 0x1;
+ int *fp = &rnp->need_future_gp[idx];
+
+ return ACCESS_ONCE(*fp);
+}
+
+/*
* Does the current CPU require a not-yet-started grace period?
* The caller must have disabled interrupts to prevent races with
* normal callback registry.
@@ -335,7 +357,7 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
if (rcu_gp_in_progress(rsp))
return 0; /* No, a grace period is already in progress. */
- if (rcu_nocb_needs_gp(rsp))
+ if (rcu_future_needs_gp(rsp))
return 1; /* Yes, a no-CBs CPU needs one. */
if (!rdp->nxttail[RCU_NEXT_TAIL])
return 0; /* No, this is a no-CBs (or offline) CPU. */
@@ -350,14 +372,6 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
}
/*
- * Return the root node of the specified rcu_state structure.
- */
-static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
-{
- return &rsp->node[0];
-}
-
-/*
* rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
*
* If the new value of the ->dynticks_nesting counter now is zero,
@@ -1672,6 +1686,8 @@ static void rsp_wakeup(struct irq_work *work)
/* Wake up rcu_gp_kthread() to start the grace period. */
wake_up(&rsp->gp_wq);
+ trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
+ "Workqueuewoken");
}
/*
@@ -1706,8 +1722,11 @@ rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
* the wakeup to interrupt context. And don't bother waking
* up the running kthread.
*/
- if (current != rsp->gp_kthread)
+ if (current != rsp->gp_kthread) {
+ trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
+ "Workqueuewake");
irq_work_queue(&rsp->wakeup_work);
+ }
}
/*
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 75dc3c39a02a..7b572c5c65e1 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -547,7 +547,6 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static void increment_cpu_stall_ticks(void);
-static int rcu_nocb_needs_gp(struct rcu_state *rsp);
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);
static void rcu_init_one_nocb(struct rcu_node *rnp);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f9c9057239a9..f60dd6ea8333 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2068,19 +2068,6 @@ static int __init parse_rcu_nocb_poll(char *arg)
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
/*
- * Do any no-CBs CPUs need another grace period?
- *
- * 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_nocb_needs_gp(struct rcu_state *rsp)
-{
- struct rcu_node *rnp = rcu_get_root(rsp);
-
- return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
-}
-
-/*
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
* grace period.
*/
@@ -2402,11 +2389,6 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
-static int rcu_nocb_needs_gp(struct rcu_state *rsp)
-{
- return 0;
-}
-
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
}
--
1.8.1.5
--
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