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Subject[PATCH v3 tip/core/rcu 08/40] rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure
Date
The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
.../RCU/Design/Data-Structures/Data-Structures.html | 9 ++++++++-
kernel/rcu/tree.c | 12 +++++-------
kernel/rcu/tree.h | 1 +
3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index d583c653a703..bf7f266e8888 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1104,6 +1104,7 @@ Its fields are as follows:
1 int dynticks_nesting;
2 int dynticks_nmi_nesting;
3 atomic_t dynticks;
+ 4 int rcu_sched_qs_mask;
</pre>

<p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1117,11 +1118,17 @@ NMIs are counted by the <tt>-&gt;dynticks_nmi_nesting</tt>
field, except that NMIs that interrupt non-dyntick-idle execution
are not counted.

-</p><p>Finally, the <tt>-&gt;dynticks</tt> field counts the corresponding
+</p><p>The <tt>-&gt;dynticks</tt> field counts the corresponding
CPU's transitions to and from dyntick-idle mode, so that this counter
has an even value when the CPU is in dyntick-idle mode and an odd
value otherwise.

+</p><p>Finally, the <tt>-&gt;rcu_sched_qs_mask</tt> field is used
+to record the fact that the RCU core code would really like to
+see a quiescent state from the corresponding CPU.
+This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
+code, which provide a momentary idle sojourn in response.
+
<table>
<tr><th>&nbsp;</th></tr>
<tr><th align="left">Quick Quiz:</th></tr>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3747277aae67..3a0703035874 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -272,8 +272,6 @@ void rcu_bh_qs(void)
}
}

-static DEFINE_PER_CPU(int, rcu_sched_qs_mask);
-
/*
* Steal a bit from the bottom of ->dynticks for idle entry/exit
* control. Initially this is for TLB flushing.
@@ -464,8 +462,8 @@ static void rcu_momentary_dyntick_idle(void)
* Yes, we can lose flag-setting operations. This is OK, because
* the flag will be set again after some delay.
*/
- resched_mask = raw_cpu_read(rcu_sched_qs_mask);
- raw_cpu_write(rcu_sched_qs_mask, 0);
+ resched_mask = raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask);
+ raw_cpu_write(rcu_dynticks.rcu_sched_qs_mask, 0);

/* Find the flavor that needs a quiescent state. */
for_each_rcu_flavor(rsp) {
@@ -499,7 +497,7 @@ void rcu_note_context_switch(void)
trace_rcu_utilization(TPS("Start context switch"));
rcu_sched_qs();
rcu_preempt_note_context_switch();
- if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
+ if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask)))
rcu_momentary_dyntick_idle();
trace_rcu_utilization(TPS("End context switch"));
barrier(); /* Avoid RCU read-side critical sections leaking up. */
@@ -524,7 +522,7 @@ void rcu_all_qs(void)
unsigned long flags;

barrier(); /* Avoid RCU read-side critical sections leaking down. */
- if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) {
+ if (unlikely(raw_cpu_read(rcu_dynticks.rcu_sched_qs_mask))) {
local_irq_save(flags);
rcu_momentary_dyntick_idle();
local_irq_restore(flags);
@@ -1351,7 +1349,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
* is set too high, we override with half of the RCU CPU stall
* warning delay.
*/
- rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu);
+ rcrmp = &per_cpu(rcu_dynticks.rcu_sched_qs_mask, rdp->cpu);
if (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
time_after(jiffies, rdp->rsp->jiffies_resched)) {
if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) {
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 7468b4de7e0c..e298281984dc 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -113,6 +113,7 @@ struct rcu_dynticks {
/* Process level is worth LLONG_MAX/2. */
int dynticks_nmi_nesting; /* Track NMI nesting level. */
atomic_t dynticks; /* Even value for idle, else odd. */
+ int rcu_sched_qs_mask; /* GP old, need quiescent state. */
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
long long dynticks_idle_nesting;
/* irq/process nesting level from idle. */
--
2.5.2
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