From f2b1760aedba1d8394636ba31b9e864e82527528 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 24 Oct 2017 08:42:41 -0700 Subject: 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 --- 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 rcu_qs_ctr_snap field is used to detect cases where a given operation has resulted in a quiescent state -for all flavors of RCU, for example, cond_resched_rcu_qs(). +for all flavors of RCU, for example, cond_resched() +when RCU has indicated a need for quiescent states.
RCU Callback Handling
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 CONFIG_NO_HZ_FULL=y) or in the kernel. That said, CPU-bound loops in the kernel must execute -cond_resched_rcu_qs() at least once per few tens of milliseconds +cond_resched() at least once per few tens of milliseconds in order to avoid receiving an IPI from RCU.

@@ -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 schedule(), -cond_resched_rcu_qs(), and +cond_resched(), and synchronize_rcu_tasks(). 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, -- cgit v1.2.3-59-g8ed1b