This commit records RCU's responsibility to avoid degrading latencies
of CPUs running tight loops within properly configured workloads,
both in kernel and in userspace.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
Documentation/RCU/Design/Requirements/Requirements.html | 10 +++++++++-
Documentation/RCU/Design/Requirements/Requirements.htmlx | 8 ++++++++
2 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html
b/Documentation/RCU/Design/Requirements/Requirements.html
index a725f9900ec8..3004baa71bcc 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -1,5 +1,5 @@
<!-- DO NOT HAND EDIT. -->
-<!-- Instead, edit Documentation/RCU/Design/Requirements/Requirements.htmlx
and run 'sh htmlqqz.sh Documentation/RCU/Design/Requirements/Requirements' -->
+<!-- Instead, edit Requirements.htmlx and run 'sh htmlqqz.sh Requirements' -->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd";>
<html>
@@ -2171,6 +2171,14 @@ This real-time requirement motivated the grace-period
kthread, which
also simplified handling of a number of race conditions.
<p>
+RCU must avoid degrading real-time response for CPU-bound threads, whether
+executing in usermode (which is one use case for
+<tt>CONFIG_NO_HZ_FULL=y</tt>) or in the kernel.
+That said, CPU-bound loops in the kernel must execute
+<tt>cond_resched_rcu_qs()</tt> at least once per few tens of milliseconds
+in order to avoid receiving an IPI from RCU.
+
+<p>
Finally, RCU's status as a synchronization primitive means that
any RCU failure can result in arbitrary memory corruption that can be
extremely difficult to debug.
diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx
b/Documentation/RCU/Design/Requirements/Requirements.htmlx
index 3a97ba490c42..61caffc86823 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.htmlx
+++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx
@@ -2338,6 +2338,14 @@ This real-time requirement motivated the grace-period
kthread, which
also simplified handling of a number of race conditions.
<p>
+RCU must avoid degrading real-time response for CPU-bound threads, whether
+executing in usermode (which is one use case for
+<tt>CONFIG_NO_HZ_FULL=y</tt>) or in the kernel.
+That said, CPU-bound loops in the kernel must execute
+<tt>cond_resched_rcu_qs()</tt> at least once per few tens of milliseconds
+in order to avoid receiving an IPI from RCU.
+
+<p>
Finally, RCU's status as a synchronization primitive means that
any RCU failure can result in arbitrary memory corruption that can be
extremely difficult to debug.
--
2.5.2
