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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-01-26 16:18:07 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-18 11:38:17 -0700
commit9577df9a3122af08fff84b8a1a60dccf524a3891 (patch)
tree3c5f01e4cbdef694343d839b696a5ecbeb66472f /Documentation
parentabb06b99484a9f5af05c7147c289faf835f68e8e (diff)
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rcu: Pull rcu_qs_ctr into rcu_dynticks structure
The rcu_qs_ctr 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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/RCU/Design/Data-Structures/Data-Structures.html12
1 files changed, 10 insertions, 2 deletions
diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index bf7f266e8888..3d0311657533 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1105,6 +1105,7 @@ Its fields are as follows:
2 int dynticks_nmi_nesting;
3 atomic_t dynticks;
4 int rcu_sched_qs_mask;
+ 5 unsigned long rcu_qs_ctr;
</pre>
<p>The <tt>-&gt;dynticks_nesting</tt> field counts the
@@ -1123,12 +1124,19 @@ 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
+</p><p>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.
+see a quiescent state from the corresponding CPU, so much so that
+it is willing to call for heavy-weight dyntick-counter operations.
This flag is checked by RCU's context-switch and <tt>cond_resched()</tt>
code, which provide a momentary idle sojourn in response.
+</p><p>Finally the <tt>-&gt;rcu_qs_ctr</tt> field is used to record
+quiescent states from <tt>cond_resched()</tt>.
+Because <tt>cond_resched()</tt> can execute quite frequently, this
+must be quite lightweight, as in a non-atomic increment of this
+per-CPU field.
+
<table>
<tr><th>&nbsp;</th></tr>
<tr><th align="left">Quick Quiz:</th></tr>