linux-kernel - [PATCH RFC tip/core/rcu 4/6] rcu: Clarify help text for RCU_BOOST

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 23 Apr 2012 09:42:25 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH RFC tip/core/rcu 4/6] rcu: Clarify help text for RCU_BOOST_PRIO

From: "Paul E. McKenney" <paul.mckenney@...aro.org>

The old text confused real-time applications with real-time threads, so
that you pretty much needed to understand how this kernel configuration
parameter worked to understand the help text.  This commit therefore
attempts to make the help text human-readable.

Reported-by: Jörn Engel <joern@...estorage.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 init/Kconfig |   23 +++++++++++++++++++----
 1 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 6cfd71d..85c6870 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -515,10 +515,25 @@ config RCU_BOOST_PRIO
 	depends on RCU_BOOST
 	default 1
 	help
-	  This option specifies the real-time priority to which preempted
-	  RCU readers are to be boosted.  If you are working with CPU-bound
-	  real-time applications, you should specify a priority higher then
-	  the highest-priority CPU-bound application.
+	  This option specifies the real-time priority to which long-term
+	  preempted RCU readers are to be boosted.  If you are working
+	  with a real-time application that has one or more CPU-bound
+	  threads running at a real-time priority level, you should set
+	  RCU_BOOST_PRIO to a priority higher then the highest-priority
+	  real-time CPU-bound thread.  The default RCU_BOOST_PRIO value
+	  of 1 is appropriate in the common case, which is real-time
+	  applications that do not have any CPU-bound threads.
+
+	  Some real-time applications might not have a single real-time
+	  thread that saturates a given CPU, but instead might have
+	  multiple real-time threads that, taken together, fully utilize
+	  that CPU.  In this case, you should set RCU_BOOST_PRIO to
+	  a priority higher than the lowest-priority thread that is
+	  conspiring to prevent the CPU from running any non-real-time
+	  tasks.  For example, if one thread at priority 10 and another
+	  thread at priority 5 are between themselves fully consuming
+	  the CPU time on a given CPU, then RCU_BOOST_PRIO should be
+	  set to priority 6 or higher.
 
 	  Specify the real-time priority, or take the default if unsure.
 
-- 
1.7.8

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/