Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit f2b1760a authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 388a4c88

Documentation/RCU/Design/Data-Structures/Data-Structures.html

+2 −1
Original line number Diff line number Diff line
@@ -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>

Documentation/RCU/Design/Requirements/Requirements.html

+2 −2
Original line number Diff line number Diff line
@@ -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.

Documentation/RCU/stallwarn.txt

+4 −6
Original line number Diff line number Diff line
@@ -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,