The config option `CONFIG_PREEMPT' is used for the preemption model "Low-Latency Desktop". The config option `CONFIG_PREEMPTION' is enabled when kernel preemption is enabled which is true for the `CONFIG_PREEMPT' and `CONFIG_PREEMPT_RT' preemption models.
Use `CONFIG_PREEMPTION' if it applies to both preemption models and not just to `CONFIG_PREEMPT'. Cc: "Paul E. McKenney" <paul...@kernel.org> Cc: Josh Triplett <j...@joshtriplett.org> Cc: Steven Rostedt <rost...@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> Cc: Lai Jiangshan <jiangshan...@gmail.com> Cc: Joel Fernandes <j...@joelfernandes.org> Cc: linux-doc@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> --- .../Expedited-Grace-Periods.html | 8 +++---- .../RCU/Design/Requirements/Requirements.html | 24 +++++++++---------- Documentation/RCU/checklist.txt | 4 ++-- Documentation/RCU/rcubarrier.txt | 8 +++---- Documentation/RCU/stallwarn.txt | 4 ++-- Documentation/RCU/whatisRCU.txt | 7 +++--- 6 files changed, 28 insertions(+), 27 deletions(-) diff --git a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html index 57300db4b5ff6..31c99382994e0 100644 --- a/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html +++ b/Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html @@ -56,8 +56,8 @@ sections. RCU-preempt Expedited Grace Periods</a></h2> <p> -<tt>CONFIG_PREEMPT=y</tt> kernels implement RCU-preempt. -The overall flow of the handling of a given CPU by an RCU-preempt +<tt>CONFIG_PREEMPT=y</tt> and <tt>CONFIG_PREEMPT_RT=y</tt> kernels implement +RCU-preempt. The overall flow of the handling of a given CPU by an RCU-preempt expedited grace period is shown in the following diagram: <p><img src="ExpRCUFlow.svg" alt="ExpRCUFlow.svg" width="55%"> @@ -140,8 +140,8 @@ or offline, among other things. RCU-sched Expedited Grace Periods</a></h2> <p> -<tt>CONFIG_PREEMPT=n</tt> kernels implement RCU-sched. -The overall flow of the handling of a given CPU by an RCU-sched +<tt>CONFIG_PREEMPT=n</tt> and <tt>CONFIG_PREEMPT_RT=n</tt> kernels implement +RCU-sched. The overall flow of the handling of a given CPU by an RCU-sched expedited grace period is shown in the following diagram: <p><img src="ExpSchedFlow.svg" alt="ExpSchedFlow.svg" width="55%"> diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 467251f7fef69..348c5db1ff2bb 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -106,7 +106,7 @@ big RCU read-side critical section. Production-quality implementations of <tt>rcu_read_lock()</tt> and <tt>rcu_read_unlock()</tt> are extremely lightweight, and in fact have exactly zero overhead in Linux kernels built for production -use with <tt>CONFIG_PREEMPT=n</tt>. +use with <tt>CONFIG_PREEMPTION=n</tt>. <p> This guarantee allows ordering to be enforced with extremely low @@ -1499,7 +1499,7 @@ costs have plummeted. However, as I learned from Matt Mackall's <a href="http://elinux.org/Linux_Tiny-FAQ";>bloatwatch</a> efforts, memory footprint is critically important on single-CPU systems with -non-preemptible (<tt>CONFIG_PREEMPT=n</tt>) kernels, and thus +non-preemptible (<tt>CONFIG_PREEMPTION=n</tt>) kernels, and thus <a href="https://lkml.kernel.org/g/20090113221724.ga15...@linux.vnet.ibm.com";>tiny RCU</a> was born. Josh Triplett has since taken over the small-memory banner with his @@ -1887,7 +1887,7 @@ constructs, there are limitations. <p> Implementations of RCU for which <tt>rcu_read_lock()</tt> and <tt>rcu_read_unlock()</tt> generate no code, such as -Linux-kernel RCU when <tt>CONFIG_PREEMPT=n</tt>, can be +Linux-kernel RCU when <tt>CONFIG_PREEMPTION=n</tt>, can be nested arbitrarily deeply. After all, there is no overhead. Except that if all these instances of <tt>rcu_read_lock()</tt> @@ -2229,7 +2229,7 @@ be a no-op. <p> However, once the scheduler has spawned its first kthread, this early boot trick fails for <tt>synchronize_rcu()</tt> (as well as for -<tt>synchronize_rcu_expedited()</tt>) in <tt>CONFIG_PREEMPT=y</tt> +<tt>synchronize_rcu_expedited()</tt>) in <tt>CONFIG_PREEMPTION=y</tt> kernels. The reason is that an RCU read-side critical section might be preempted, which means that a subsequent <tt>synchronize_rcu()</tt> really does have @@ -2568,7 +2568,7 @@ The compiler must not be permitted to transform this source code into <p> If the compiler did make this transformation in a -<tt>CONFIG_PREEMPT=n</tt> kernel build, and if <tt>get_user()</tt> did +<tt>CONFIG_PREEMPTION=n</tt> kernel build, and if <tt>get_user()</tt> did page fault, the result would be a quiescent state in the middle of an RCU read-side critical section. This misplaced quiescent state could result in line 4 being @@ -2906,7 +2906,7 @@ in conjunction with the The real-time-latency response requirements are such that the traditional approach of disabling preemption across RCU read-side critical sections is inappropriate. -Kernels built with <tt>CONFIG_PREEMPT=y</tt> therefore +Kernels built with <tt>CONFIG_PREEMPTION=y</tt> therefore use an RCU implementation that allows RCU read-side critical sections to be preempted. This requirement made its presence known after users made it @@ -3064,7 +3064,7 @@ includes <tt>rcu_barrier_bh()</tt>, and <tt>rcu_read_lock_bh_held()</tt>. However, the update-side APIs are now simple wrappers for other RCU -flavors, namely RCU-sched in CONFIG_PREEMPT=n kernels and RCU-preempt +flavors, namely RCU-sched in CONFIG_PREEMPTION=n kernels and RCU-preempt otherwise. <h3><a name="Sched Flavor">Sched Flavor (Historical)</a></h3> @@ -3088,12 +3088,12 @@ of an RCU read-side critical section can be a quiescent state. Therefore, <i>RCU-sched</i> was created, which follows “classic” RCU in that an RCU-sched grace period waits for for pre-existing interrupt and NMI handlers. -In kernels built with <tt>CONFIG_PREEMPT=n</tt>, the RCU and RCU-sched +In kernels built with <tt>CONFIG_PREEMPTION=n</tt>, the RCU and RCU-sched APIs have identical implementations, while kernels built with -<tt>CONFIG_PREEMPT=y</tt> provide a separate implementation for each. +<tt>CONFIG_PREEMPTION=y</tt> provide a separate implementation for each. <p> -Note well that in <tt>CONFIG_PREEMPT=y</tt> kernels, +Note well that in <tt>CONFIG_PREEMPTION=y</tt> kernels, <tt>rcu_read_lock_sched()</tt> and <tt>rcu_read_unlock_sched()</tt> disable and re-enable preemption, respectively. This means that if there was a preemption attempt during the @@ -3302,12 +3302,12 @@ The tasks-RCU API is quite compact, consisting only of <tt>call_rcu_tasks()</tt>, <tt>synchronize_rcu_tasks()</tt>, and <tt>rcu_barrier_tasks()</tt>. -In <tt>CONFIG_PREEMPT=n</tt> kernels, trampolines cannot be preempted, +In <tt>CONFIG_PREEMPTION=n</tt> kernels, trampolines cannot be preempted, so these APIs map to <tt>call_rcu()</tt>, <tt>synchronize_rcu()</tt>, and <tt>rcu_barrier()</tt>, respectively. -In <tt>CONFIG_PREEMPT=y</tt> kernels, trampolines can be preempted, +In <tt>CONFIG_PREEMPTION=y</tt> kernels, trampolines can be preempted, and these three APIs are therefore implemented by separate functions that check for voluntary context switches. diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index e98ff261a438b..087dc6c22c37c 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -210,8 +210,8 @@ over a rather long period of time, but improvements are always welcome! the rest of the system. 7. As of v4.20, a given kernel implements only one RCU flavor, - which is RCU-sched for PREEMPT=n and RCU-preempt for PREEMPT=y. - If the updater uses call_rcu() or synchronize_rcu(), + which is RCU-sched for PREEMPTION=n and RCU-preempt for + PREEMPTION=y. If the updater uses call_rcu() or synchronize_rcu(), then the corresponding readers my use rcu_read_lock() and rcu_read_unlock(), rcu_read_lock_bh() and rcu_read_unlock_bh(), or any pair of primitives that disables and re-enables preemption, diff --git a/Documentation/RCU/rcubarrier.txt b/Documentation/RCU/rcubarrier.txt index a2782df697328..5aa93c215af46 100644 --- a/Documentation/RCU/rcubarrier.txt +++ b/Documentation/RCU/rcubarrier.txt @@ -6,8 +6,8 @@ RCU (read-copy update) is a synchronization mechanism that can be thought of as a replacement for read-writer locking (among other things), but with very low-overhead readers that are immune to deadlock, priority inversion, and unbounded latency. RCU read-side critical sections are delimited -by rcu_read_lock() and rcu_read_unlock(), which, in non-CONFIG_PREEMPT -kernels, generate no code whatsoever. +by rcu_read_lock() and rcu_read_unlock(), which, in +non-CONFIG_PREEMPTION kernels, generate no code whatsoever. This means that RCU writers are unaware of the presence of concurrent readers, so that RCU updates to shared data must be undertaken quite @@ -303,10 +303,10 @@ Answer: This cannot happen. The reason is that on_each_cpu() has its last to smp_call_function() and further to smp_call_function_on_cpu(), causing this latter to spin until the cross-CPU invocation of rcu_barrier_func() has completed. This by itself would prevent - a grace period from completing on non-CONFIG_PREEMPT kernels, + a grace period from completing on non-CONFIG_PREEMPTION kernels, since each CPU must undergo a context switch (or other quiescent state) before the grace period can complete. However, this is - of no use in CONFIG_PREEMPT kernels. + of no use in CONFIG_PREEMPTION kernels. Therefore, on_each_cpu() disables preemption across its call to smp_call_function() and also across the local call to diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index f48f4621ccbc2..bd510771b75ec 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -20,7 +20,7 @@ o A CPU looping with preemption disabled. o A CPU looping with bottom halves disabled. -o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the kernel +o For !CONFIG_PREEMPTION 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(). @@ -39,7 +39,7 @@ o Anything that prevents RCU's grace-period kthreads from running. result in the "rcu_.*kthread starved for" console-log message, which will include additional debugging information. -o A CPU-bound real-time task in a CONFIG_PREEMPT kernel, which might +o A CPU-bound real-time task in a CONFIG_PREEMPTION kernel, which might happen to preempt a low-priority task in the middle of an RCU read-side critical section. This is especially damaging if that low-priority task is not permitted to run on any other CPU, diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 7e1a8721637ab..7e03e8f80b293 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -648,9 +648,10 @@ Quick Quiz #1: Why is this argument naive? How could a deadlock This section presents a "toy" RCU implementation that is based on "classic RCU". It is also short on performance (but only for updates) and -on features such as hotplug CPU and the ability to run in CONFIG_PREEMPT -kernels. The definitions of rcu_dereference() and rcu_assign_pointer() -are the same as those shown in the preceding section, so they are omitted. +on features such as hotplug CPU and the ability to run in +CONFIG_PREEMPTION kernels. The definitions of rcu_dereference() and +rcu_assign_pointer() are the same as those shown in the preceding +section, so they are omitted. void rcu_read_lock(void) { } -- 2.23.0
