diff options
author | Paul E. McKenney <paulmck@kernel.org> | 2022-02-17 12:26:00 -0800 |
---|---|---|
committer | Paul E. McKenney <paulmck@kernel.org> | 2022-04-20 15:57:02 -0700 |
commit | 6172de3c7f1171e55314bfc5ee4ae6edd225b048 (patch) | |
tree | 5d789928c265a96f5e88bba489d821a09d7f0771 /Documentation | |
parent | 3123109284176b1532874591f7c81f3837bbdc17 (diff) | |
download | linux-stable-6172de3c7f1171e55314bfc5ee4ae6edd225b048.tar.gz linux-stable-6172de3c7f1171e55314bfc5ee4ae6edd225b048.tar.bz2 linux-stable-6172de3c7f1171e55314bfc5ee4ae6edd225b048.zip |
docs: Add documentation for rude and trace RCU flavors
This commit belatedly adds documentation of Tasks Rude RCU and Tasks
Trace RCU to RCU's requirements document.
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.rst | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index 45278e2974c0..ff2be1ac54c4 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2654,6 +2654,38 @@ synchronize_rcu(), and rcu_barrier(), respectively. In three APIs are therefore implemented by separate functions that check for voluntary context switches. +Tasks Rude RCU +~~~~~~~~~~~~~~ + +Some forms of tracing need to wait for all preemption-disabled regions +of code running on any online CPU, including those executed when RCU is +not watching. This means that synchronize_rcu() is insufficient, and +Tasks Rude RCU must be used instead. This flavor of RCU does its work by +forcing a workqueue to be scheduled on each online CPU, hence the "Rude" +moniker. And this operation is considered to be quite rude by real-time +workloads that don't want their ``nohz_full`` CPUs receiving IPIs and +by battery-powered systems that don't want their idle CPUs to be awakened. + +The tasks-rude-RCU API is also reader-marking-free and thus quite compact, +consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(), +and rcu_barrier_tasks_rude(). + +Tasks Trace RCU +~~~~~~~~~~~~~~~ + +Some forms of tracing need to sleep in readers, but cannot tolerate +SRCU's read-side overhead, which includes a full memory barrier in both +srcu_read_lock() and srcu_read_unlock(). This need is handled by a +Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with +readers. Real-time systems that cannot tolerate IPIs may build their +kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=y``, which avoids the IPIs at +the expense of adding full memory barriers to the read-side primitives. + +The tasks-trace-RCU API is also reasonably compact, +consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(), +rcu_read_lock_trace_held(), call_rcu_tasks_trace(), +synchronize_rcu_tasks_trace(), and rcu_barrier_tasks_trace(). + Possible Future Changes ----------------------- |