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Commit 41abcf32 authored by Paul E. McKenney's avatar Paul E. McKenney
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documentation: Add real-time requirements from CPU-bound workloads 

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 70946a44
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Documentation/RCU/Design/Requirements/Requirements.html
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<!-- DO NOT HAND EDIT. --> <!-- 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" <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd"> "http://www.w3.org/TR/html4/loose.dtd">
<html> <html>
...@@ -2170,6 +2170,14 @@ up to and including systems with 4096 CPUs. ...@@ -2170,6 +2170,14 @@ up to and including systems with 4096 CPUs.
This real-time requirement motivated the grace-period kthread, which This real-time requirement motivated the grace-period kthread, which
also simplified handling of a number of race conditions. 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> <p>
Finally, RCU's status as a synchronization primitive means that Finally, RCU's status as a synchronization primitive means that
any RCU failure can result in arbitrary memory corruption that can be any RCU failure can result in arbitrary memory corruption that can be
......
Documentation/RCU/Design/Requirements/Requirements.htmlx
View file @ 41abcf32
...@@ -2337,6 +2337,14 @@ up to and including systems with 4096 CPUs. ...@@ -2337,6 +2337,14 @@ up to and including systems with 4096 CPUs.
This real-time requirement motivated the grace-period kthread, which This real-time requirement motivated the grace-period kthread, which
also simplified handling of a number of race conditions. 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> <p>
Finally, RCU's status as a synchronization primitive means that Finally, RCU's status as a synchronization primitive means that
any RCU failure can result in arbitrary memory corruption that can be any RCU failure can result in arbitrary memory corruption that can be
......
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