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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: linux-kernel@vger.kernel.org
Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
	fweisbec@gmail.com, oleg@redhat.com,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 09/10] doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()
Date: Fri,  1 Dec 2017 11:21:43 -0800	[thread overview]
Message-ID: <1512156104-20104-9-git-send-email-paulmck@linux.vnet.ibm.com> (raw)
In-Reply-To: <20171201192122.GA19301@linux.vnet.ibm.com>

Now that cond_resched() also provides RCU quiescent states when
needed, it can be used in place of cond_resched_rcu_qs().  This
commit therefore documents this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 Documentation/RCU/Design/Data-Structures/Data-Structures.html |  3 ++-
 Documentation/RCU/Design/Requirements/Requirements.html       |  4 ++--
 Documentation/RCU/stallwarn.txt                               | 10 ++++------
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index 38d6d800761f..412466e4967a 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -1097,7 +1097,8 @@ will cause the CPU to disregard the values of its counters on
 its next exit from idle.
 Finally, the <tt>rcu_qs_ctr_snap</tt> field is used to detect
 cases where a given operation has resulted in a quiescent state
-for all flavors of RCU, for example, <tt>cond_resched_rcu_qs()</tt>.
+for all flavors of RCU, for example, <tt>cond_resched()</tt>
+when RCU has indicated a need for quiescent states.
 
 <h5>RCU Callback Handling</h5>
 
diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html
index 62e847bcdcdd..0372e6c54eef 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.html
+++ b/Documentation/RCU/Design/Requirements/Requirements.html
@@ -2797,7 +2797,7 @@ 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
+<tt>cond_resched()</tt> at least once per few tens of milliseconds
 in order to avoid receiving an IPI from RCU.
 
 <p>
@@ -3128,7 +3128,7 @@ The solution, in the form of
 is to have implicit
 read-side critical sections that are delimited by voluntary context
 switches, that is, calls to <tt>schedule()</tt>,
-<tt>cond_resched_rcu_qs()</tt>, and
+<tt>cond_resched()</tt>, and
 <tt>synchronize_rcu_tasks()</tt>.
 In addition, transitions to and from userspace execution also delimit
 tasks-RCU read-side critical sections.
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index a08f928c8557..4259f95c3261 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -23,12 +23,10 @@ o	A CPU looping with preemption disabled.  This condition can
 o	A CPU looping with bottom halves disabled.  This condition can
 	result in RCU-sched and RCU-bh stalls.
 
-o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
-	kernel without invoking schedule().  Note that cond_resched()
-	does not necessarily prevent RCU CPU stall warnings.  Therefore,
-	if the looping in the kernel is really expected and desirable
-	behavior, you might need to replace some of the cond_resched()
-	calls with calls to cond_resched_rcu_qs().
+o	For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel
+	without invoking schedule().  If the looping in the kernel is
+	really expected and desirable behavior, you might need to add
+	some calls to cond_resched().
 
 o	Booting Linux using a console connection that is too slow to
 	keep up with the boot-time console-message rate.  For example,
-- 
2.5.2

  parent reply	other threads:[~2017-12-01 19:21 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-01 19:21 [PATCH tip/core/rcu 0/10] Don not IPI offline CPUs, de-emphasize cond_resched_rcu_qs() Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 01/10] sched: Stop resched_cpu() from sending IPIs to offline CPUs Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 02/10] sched: Stop switched_to_rt() " Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 03/10] netfilter: Eliminate cond_resched_rcu_qs() in favor of cond_resched() Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 04/10] mm: " Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 05/10] workqueue: " Paul E. McKenney
2017-12-02  1:06   ` Lai Jiangshan
2017-12-04 18:28     ` Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 06/10] trace: " Paul E. McKenney
2018-02-24 20:12   ` Steven Rostedt
2018-02-25 17:49     ` Paul E. McKenney
2018-02-25 18:17       ` Paul E. McKenney
2018-02-25 18:39         ` Paul E. McKenney
2018-02-27  2:29           ` Steven Rostedt
2018-02-27 15:36             ` Paul E. McKenney
2018-02-28 23:12               ` Steven Rostedt
2018-03-01  1:21                 ` Paul E. McKenney
2018-03-01  5:04                   ` Steven Rostedt
2018-03-01 20:48                     ` Paul E. McKenney
2018-03-02 20:06                       ` Steven Rostedt
2018-03-03  0:54                         ` Paul E. McKenney
2018-02-26  4:57         ` Steven Rostedt
2018-02-26  5:47           ` Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 07/10] softirq: " Paul E. McKenney
2017-12-01 19:21 ` [PATCH tip/core/rcu 08/10] fs: " Paul E. McKenney
2017-12-01 19:21 ` Paul E. McKenney [this message]
2017-12-01 19:21 ` [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond_resched() Paul E. McKenney
2017-12-02  8:56   ` Peter Zijlstra
2017-12-02 12:22     ` Paul E. McKenney
2017-12-02 13:55       ` Peter Zijlstra
2018-02-24 20:18       ` Steven Rostedt
2018-02-25 17:52         ` Paul E. McKenney

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