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Groups > linux.kernel > #1341507

[PATCH tip/core/rcu 01/14] documentation: Add real-time requirements from CPU-bound workloads

From "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Newsgroups linux.kernel
Subject [PATCH tip/core/rcu 01/14] documentation: Add real-time requirements from CPU-bound workloads
Date 2016-02-24 06:10 +0100
Message-ID <r5zS2-84d-13@gated-at.bofh.it> (permalink)
References <r5zS2-84d-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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 <paulmck@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

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[PATCH tip/core/rcu 0/14] Documentation updates for 4.6 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 01/14] documentation:  Add real-time requirements from CPU-bound workloads "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 14/14] documentation: Clarify compiler store-fusion example "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 12/14] documentation: Document illegality of call_rcu() from offline CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 07/14] documentation: Distinguish between local and global transitivity "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 05/14] documentation: Remove obsolete reference to RCU-protected indexes "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 08/14] documentation:  Add alternative release-acquire outcome "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 11/14] documentation: Transitivity is not cumulativity "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 04/14] documentation: Add synchronize_rcu_mult() to the requirements "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:10 +0100
  [PATCH tip/core/rcu 13/14] documentation: Explain how RCU's combining tree fights contention "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 10/14] documentation: Explain why rcu_read_lock() needs no barrier() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 03/14] documentation: Fix memory-barriers.txt section references "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
  [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100
    Re: [PATCH tip/core/rcu 02/14] documentation: Fix control  dependency and identical stores Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2016-02-24 22:20 +0100
      Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 22:50 +0100
        Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Jianyu Zhan <nasa4836@gmail.com> - 2016-02-25 07:50 +0100
          Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 15:10 +0100
        Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Peter Zijlstra <peterz@infradead.org> - 2016-02-25 09:30 +0100
          Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 15:10 +0100
            Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores Peter Zijlstra <peterz@infradead.org> - 2016-02-25 15:50 +0100
              Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency  and identical stores "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-25 16:50 +0100
  [PATCH tip/core/rcu 06/14] documentation: Subsequent writes ordered by rcu_dereference() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-02-24 06:20 +0100

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