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doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched() 

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>
This commit is contained in:
Paul E. McKenney 2017-10-24 08:42:41 -07:00
parent 388a4c8806
commit f2b1760aed
3 changed files with 8 additions and 9 deletions
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3
Documentation/RCU/Design/Data-Structures/Data-Structures.html
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@ -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>

4
Documentation/RCU/Design/Requirements/Requirements.html
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@ -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.

10
Documentation/RCU/stallwarn.txt
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@ -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,