On Wed, Nov 06, 2019 at 04:42:34AM +0700, Phong Tran wrote: > o Adding more crossrefs. > o Bold some words. > o Add header levels. > > Signed-off-by: Phong Tran <tranmanphong@xxxxxxxxx> > --- > Documentation/RCU/whatisRCU.rst | 67 ++++++++++++++++++++------------- > 1 file changed, 41 insertions(+), 26 deletions(-) > > diff --git a/Documentation/RCU/whatisRCU.rst b/Documentation/RCU/whatisRCU.rst > index ae40c8bcc56c..3e24e0155a91 100644 > --- a/Documentation/RCU/whatisRCU.rst > +++ b/Documentation/RCU/whatisRCU.rst > @@ -150,7 +150,7 @@ later. See the kernel docbook documentation for more info, or look directly > at the function header comments. > > rcu_read_lock() > - > +^^^^^^^^^^^^^^^ > void rcu_read_lock(void); > > Used by a reader to inform the reclaimer that the reader is > @@ -164,7 +164,7 @@ rcu_read_lock() > longer-term references to data structures. > > rcu_read_unlock() > - > +^^^^^^^^^^^^^^^^^ > void rcu_read_unlock(void); > > Used by a reader to inform the reclaimer that the reader is > @@ -172,13 +172,13 @@ rcu_read_unlock() > read-side critical sections may be nested and/or overlapping. > > synchronize_rcu() > - > +^^^^^^^^^^^^^^^^^ > void synchronize_rcu(void); > > Marks the end of updater code and the beginning of reclaimer > code. It does this by blocking until all pre-existing RCU > read-side critical sections on all CPUs have completed. > - Note that synchronize_rcu() will -not- necessarily wait for > + Note that synchronize_rcu() will **not** necessarily wait for > any subsequent RCU read-side critical sections to complete. > For example, consider the following sequence of events:: > > @@ -196,7 +196,7 @@ synchronize_rcu() > any that begin after synchronize_rcu() is invoked. > > Of course, synchronize_rcu() does not necessarily return > - -immediately- after the last pre-existing RCU read-side critical > + **immediately** after the last pre-existing RCU read-side critical > section completes. For one thing, there might well be scheduling > delays. For another thing, many RCU implementations process > requests in batches in order to improve efficiencies, which can > @@ -225,10 +225,10 @@ synchronize_rcu() > checklist.txt for some approaches to limiting the update rate. > > rcu_assign_pointer() > - > +^^^^^^^^^^^^^^^^^^^^ > void rcu_assign_pointer(p, typeof(p) v); > > - Yes, rcu_assign_pointer() -is- implemented as a macro, though it > + Yes, rcu_assign_pointer() **is** implemented as a macro, though it > would be cool to be able to declare a function in this manner. > (Compiler experts will no doubt disagree.) > > @@ -245,7 +245,7 @@ rcu_assign_pointer() > the _rcu list-manipulation primitives such as list_add_rcu(). > > rcu_dereference() > - > +^^^^^^^^^^^^^^^^^ > typeof(p) rcu_dereference(p); > > Like rcu_assign_pointer(), rcu_dereference() must be implemented > @@ -280,8 +280,8 @@ rcu_dereference() > unnecessary overhead on Alpha CPUs. > > Note that the value returned by rcu_dereference() is valid > - only within the enclosing RCU read-side critical section [1]. > - For example, the following is -not- legal:: > + only within the enclosing RCU read-side critical section [1]_. > + For example, the following is **not** legal:: > > rcu_read_lock(); > p = rcu_dereference(head.next); > @@ -304,9 +304,11 @@ rcu_dereference() > at any time, including immediately after the rcu_dereference(). > And, again like rcu_assign_pointer(), rcu_dereference() is > typically used indirectly, via the _rcu list-manipulation > - primitives, such as list_for_each_entry_rcu() [2]. > + primitives, such as list_for_each_entry_rcu() [2]_. > + > + .. [1] Hey Phong, I just checked the patch but this change doesn't seem quite right. It just creates an empty footnote. Something on the lines of .. [1] The variant rcu_dereference_protected()... should work. > > - [1] The variant rcu_dereference_protected() can be used outside > + The variant rcu_dereference_protected() can be used outside > of an RCU read-side critical section as long as the usage is > protected by locks acquired by the update-side code. This variant > avoids the lockdep warning that would happen when using (for > @@ -319,7 +321,9 @@ rcu_dereference() > a lockdep splat is emitted. See Documentation/RCU/Design/Requirements/Requirements.rst > and the API's code comments for more details and example usage. > > - [2] If the list_for_each_entry_rcu() instance might be used by > + .. [2] Similarly for this. > + > + If the list_for_each_entry_rcu() instance might be used by > update-side code as well as by RCU readers, then an additional > lockdep expression can be added to its list of arguments. > For example, given an additional "lock_is_held(&mylock)" argument, > @@ -459,22 +463,22 @@ uses of RCU may be found in :ref:`listRCU.rst <list_rcu_doc>`, > > So, to sum up: > > -o Use rcu_read_lock() and rcu_read_unlock() to guard RCU > +- Use rcu_read_lock() and rcu_read_unlock() to guard RCU > read-side critical sections. > > -o Within an RCU read-side critical section, use rcu_dereference() > +- Within an RCU read-side critical section, use rcu_dereference() > to dereference RCU-protected pointers. > > -o Use some solid scheme (such as locks or semaphores) to > +- Use some solid scheme (such as locks or semaphores) to > keep concurrent updates from interfering with each other. > > -o Use rcu_assign_pointer() to update an RCU-protected pointer. > +- Use rcu_assign_pointer() to update an RCU-protected pointer. > This primitive protects concurrent readers from the updater, > - -not- concurrent updates from each other! You therefore still > + **not** concurrent updates from each other! You therefore still > need to use locking (or something similar) to keep concurrent > rcu_assign_pointer() primitives from interfering with each other. > > -o Use synchronize_rcu() -after- removing a data element from an > +- Use synchronize_rcu() **after** removing a data element from an > RCU-protected data structure, but -before- reclaiming/freeing And this -before- is feeling lonely aswell. Thanks Amol > the data element, in order to wait for the completion of all > RCU read-side critical sections that might be referencing that > @@ -566,7 +570,7 @@ namely foo_reclaim(). > The summary of advice is the same as for the previous section, except > that we are now using call_rcu() rather than synchronize_rcu(): > > -o Use call_rcu() -after- removing a data element from an > +- Use call_rcu() **after** removing a data element from an > RCU-protected data structure in order to register a callback > function that will be invoked after the completion of all RCU > read-side critical sections that might be referencing that > @@ -603,7 +607,7 @@ more details on the current implementation as of early 2004. > > > 5A. "TOY" IMPLEMENTATION #1: LOCKING > - > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > This section presents a "toy" RCU implementation that is based on > familiar locking primitives. Its overhead makes it a non-starter for > real-life use, as does its lack of scalability. It is also unsuitable > @@ -671,6 +675,8 @@ that the only thing that can block rcu_read_lock() is a synchronize_rcu(). > But synchronize_rcu() does not acquire any locks while holding rcu_gp_mutex, > so there can be no deadlock cycle. > > +.. _quiz_1: > + > Quick Quiz #1: > Why is this argument naive? How could a deadlock > occur when using this algorithm in a real-world Linux > @@ -679,7 +685,7 @@ Quick Quiz #1: > :ref:`Answers to Quick Quiz <8_whatisRCU>` > > 5B. "TOY" EXAMPLE #2: CLASSIC RCU > - > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > 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 > @@ -710,14 +716,14 @@ CPU in turn. The run_on() primitive can be implemented straightforwardly > in terms of the sched_setaffinity() primitive. Of course, a somewhat less > "toy" implementation would restore the affinity upon completion rather > than just leaving all tasks running on the last CPU, but when I said > -"toy", I meant -toy-! > +"toy", I meant **toy**! > > So how the heck is this supposed to work??? > > Remember that it is illegal to block while in an RCU read-side critical > section. Therefore, if a given CPU executes a context switch, we know > that it must have completed all preceding RCU read-side critical sections. > -Once -all- CPUs have executed a context switch, then -all- preceding > +Once **all** CPUs have executed a context switch, then **all** preceding > RCU read-side critical sections will have completed. > > So, suppose that we remove a data item from its structure and then invoke > @@ -725,12 +731,16 @@ synchronize_rcu(). Once synchronize_rcu() returns, we are guaranteed > that there are no RCU read-side critical sections holding a reference > to that data item, so we can safely reclaim it. > > +.. _quiz_2: > + > Quick Quiz #2: > Give an example where Classic RCU's read-side > - overhead is -negative-. > + overhead is **negative**. > > :ref:`Answers to Quick Quiz <8_whatisRCU>` > > +.. _quiz_3: > + > Quick Quiz #3: > If it is illegal to block in an RCU read-side > critical section, what the heck do you do in > @@ -1076,9 +1086,11 @@ Answer: > approach where tasks in RCU read-side critical sections > cannot be blocked by tasks executing synchronize_rcu(). > > +:ref:`Back to Quick Quiz #1 <quiz_1>` > + > Quick Quiz #2: > Give an example where Classic RCU's read-side > - overhead is -negative-. > + overhead is **negative**. > > Answer: > Imagine a single-CPU system with a non-CONFIG_PREEMPT > @@ -1103,6 +1115,8 @@ Answer: > even the theoretical possibility of negative overhead for > a synchronization primitive is a bit unexpected. ;-) > > +:ref:`Back to Quick Quiz #2 <quiz_2>` > + > Quick Quiz #3: > If it is illegal to block in an RCU read-side > critical section, what the heck do you do in > @@ -1128,6 +1142,7 @@ Answer: > Besides, how does the computer know what pizza parlor > the human being went to??? > > +:ref:`Back to Quick Quiz #3 <quiz_3>` > > ACKNOWLEDGEMENTS > > -- > 2.20.1 >
