| /Documentation/RCU/ |
| D | rcu.rst | 3 RCU Concepts
6 The basic idea behind RCU (read-copy update) is to split destructive
11 since dropped their references. For example, an RCU-protected deletion
14 information on using RCU with linked lists.
19 - Why would anyone want to use RCU?
21 The advantage of RCU's two-part approach is that RCU readers need
25 on modern CPUs is what gives RCU its performance advantages
26 in read-mostly situations. The fact that RCU readers need not
30 if the RCU readers give no indication when they are done?
32 Just as with spinlocks, RCU readers are not permitted to
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| D | lockdep.rst | 4 RCU and lockdep checking
7 All flavors of RCU have lockdep checking available, so that lockdep is
8 aware of when each task enters and leaves any flavor of RCU read-side
9 critical section. Each flavor of RCU is tracked separately (but note
11 tracking to include RCU state, which can sometimes help when debugging
14 In addition, RCU provides the following primitives that check lockdep's
17 rcu_read_lock_held() for normal RCU.
18 rcu_read_lock_bh_held() for RCU-bh.
19 rcu_read_lock_sched_held() for RCU-sched.
20 rcu_read_lock_any_held() for any of normal RCU, RCU-bh, and RCU-sched.
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| D | whatisRCU.rst | 3 What is RCU? -- "Read, Copy, Update"
6 Please note that the "What is RCU?" LWN series is an excellent place
7 to start learning about RCU:
9 | 1. What is RCU, Fundamentally? https://lwn.net/Articles/262464/
10 | 2. What is RCU? Part 2: Usage https://lwn.net/Articles/263130/
11 | 3. RCU part 3: the RCU API https://lwn.net/Articles/264090/
12 | 4. The RCU API, 2010 Edition https://lwn.net/Articles/418853/
14 | 5. The RCU API, 2014 Edition https://lwn.net/Articles/609904/
16 | 6. The RCU API, 2019 Edition https://lwn.net/Articles/777036/
21 | 1. Unraveling RCU Mysteries: Fundamentals https://www.linuxfoundation.org/webinars/unrav…
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| D | RTFP.txt | 4 This document describes RCU-related publications, and is followed by
6 be found at http://www.rdrop.com/users/paulmck/RCU/. For others, browsers
9 The first thing resembling RCU was published in 1980, when Kung and Lehman
23 serialization, which is an RCU-like mechanism that relies on the presence
31 (In contrast, implementation of RCU is permitted only in software licensed
35 At first glance, this has nothing to do with RCU, but nevertheless
37 RCU implementation in DYNIX/ptx. In 1988, Barbara Liskov published
66 synchronization [HMassalinPhD]. RCU makes extremely heavy use of
91 1995 also saw the first publication of DYNIX/ptx's RCU mechanism
98 mechanism, which is quite similar to RCU [Gamsa99]. These operating
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| D | stallwarn.rst | 4 Using RCU's CPU Stall Detector
7 This document first discusses what sorts of issues RCU's CPU stall
13 What Causes RCU CPU Stall Warnings?
16 So your kernel printed an RCU CPU stall warning. The next question is
17 "What caused it?" The following problems can result in RCU CPU stall
20 - A CPU looping in an RCU read-side critical section.
37 RCU CPU stall warning messages. Especially if you have added
40 - Anything that prevents RCU's grace-period kthreads from running.
48 happen to preempt a low-priority task in the middle of an RCU
51 in which case the next RCU grace period can never complete, which
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| D | checklist.rst | 4 Review Checklist for RCU Patches
9 that make use of RCU. Violating any of the rules listed below will
14 0. Is RCU being applied to a read-mostly situation? If the data
17 performance measurements show that RCU is nonetheless the right
18 tool for the job. Yes, RCU does reduce read-side overhead by
20 of RCU will do much more reading than updating.
22 Another exception is where performance is not an issue, and RCU
27 Yet another exception is where the low real-time latency of RCU's
30 One final exception is where RCU readers are used to prevent
40 RCU does allow *readers* to run (almost) naked, but *writers* must
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| D | UP.rst | 3 RCU on Uniprocessor Systems
18 Suppose that an RCU-based algorithm scans a linked list containing
40 Suppose that an RCU-based algorithm again scans a linked list containing
45 RCU usage, since call_rcu() must wait for a grace period to elapse.
48 underlying RCU, namely that call_rcu() defers invoking its arguments until
49 all RCU read-side critical sections currently executing have completed.
85 What locking restriction must RCU callbacks respect?
89 It is important to note that userspace RCU implementations *do*
93 Nevertheless, people writing userspace RCU implementations are strongly
100 Permitting call_rcu() to immediately invoke its arguments breaks RCU,
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| D | lockdep-splat.rst | 4 Lockdep-RCU Splat
7 Lockdep-RCU was added to the Linux kernel in early 2010
9 misuses of the RCU API, most notably using one of the rcu_dereference()
10 family to access an RCU-protected pointer without the proper protection.
11 When such misuse is detected, an lockdep-RCU splat is emitted.
13 The usual cause of a lockdep-RCU splat is someone accessing an
14 RCU-protected data structure without either (1) being in the right kind of
15 RCU read-side critical section or (2) holding the right update-side lock.
20 So let's look at an example RCU lockdep splat from 3.0-rc5, one that
24 WARNING: suspicious RCU usage
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| D | rcubarrier.rst | 3 RCU and Unloadable Modules
8 RCU updaters sometimes use call_rcu() to initiate an asynchronous wait for
10 struct placed within the RCU-protected data structure and another pointer
16 call_rcu(&p->rcu, p_callback);
23 struct pstruct *p = container_of(rp, struct pstruct, rcu);
34 If we unload the module while some RCU callbacks are pending,
37 http://lwn.net/images/ns/kernel/rcu-drop.jpg.
45 heavy RCU-callback load, then some of the callbacks might be deferred in
56 outstanding RCU callbacks to complete. Please note that rcu_barrier()
57 does **not** imply synchronize_rcu(), in particular, if there are no RCU
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| D | torture.rst | 4 RCU Torture Test Operation
11 The CONFIG_RCU_TORTURE_TEST config option is available for all RCU
26 …rcu-torture:--- Start of test: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_no_idle_…
27 …rcu-torture: rtc: (null) ver: 155441 tfle: 0 rta: 155441 rtaf: 8884 rtf: 155440 rtmbe: 0…
28 rcu-torture: Reader Pipe: 727860534 34213 0 0 0 0 0 0 0 0 0
29 rcu-torture: Reader Batch: 727877838 17003 0 0 0 0 0 0 0 0 0
30 …rcu-torture: Free-Block Circulation: 155440 155440 155440 155440 155440 155440 155440 155440 1554…
31 …rcu-torture:--- End of test: SUCCESS: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_n…
36 the RCU torture test. The printk()s use KERN_ALERT, so they should
41 automatic determination as to whether RCU operated correctly.
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| D | index.rst | 6 RCU concepts
18 rcu
24 NMI-RCU
27 Design/Memory-Ordering/Tree-RCU-Memory-Ordering
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| D | listRCU.rst | 3 Using RCU to Protect Read-Mostly Linked Lists
6 One of the most common uses of RCU is protecting read-mostly linked lists
9 This document describes several list-based RCU use cases.
24 A widely used usecase for RCU lists in the kernel is lockless iteration over
54 call_rcu(&p->rcu, delayed_put_task_struct);
69 This pattern is also called an **existence lock**, since RCU refrains
73 of all RCU readers that might possibly have a reference to that object.
82 to RCU. One prominent example involves network packet routing.
94 A straightforward example of this type of RCU use case may be found in
122 This means that RCU can be easily applied to the read side, as follows::
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| D | rcu_dereference.rst | 7 important to correct use of things like RCU. To this end, the pointers
24 from your calls to rcu_dereference() and friends, thus keeping your RCU
28 to load an RCU-protected pointer, otherwise CONFIG_PROVE_RCU
80 - If you are using RCU to protect JITed functions, so that the
143 RCU-protected circular linked lists.
146 of an RCU read-side critical section, and the pointer
153 Within an RCU read-side critical section, there is little
185 That said, this situation can make certain RCU usage
188 of such an RCU usage bug is shown in the section titled
189 "EXAMPLE OF AMPLIFIED RCU-USAGE BUG".
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| /Documentation/RCU/Design/Requirements/ |
| D | Requirements.rst | 2 A Tour Through RCU's Requirements
18 Read-copy update (RCU) is a synchronization mechanism that is often used
19 as a replacement for reader-writer locking. RCU is unusual in that
20 updaters do not block readers, which means that RCU's read-side
23 this concurrency between RCU readers and updaters does raise the
24 question of exactly what RCU readers are doing, which in turn raises the
25 question of exactly what RCU's requirements are.
27 This document therefore summarizes RCU's requirements, and can be
28 thought of as an informal, high-level specification for RCU. It is
29 important to understand that RCU's specification is primarily empirical
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| /Documentation/devicetree/bindings/phy/ |
| D | lantiq,vrx200-pcie-phy.yaml | 45 lantiq,rcu:
47 description: phandle to the RCU syscon
49 lantiq,rcu-endian-offset:
51 description: the offset of the endian registers for this PHY instance in the RCU syscon
53 lantiq,rcu-big-endian-mask:
73 - lantiq,rcu
74 - lantiq,rcu-endian-offset
75 - lantiq,rcu-big-endian-mask
84 lantiq,rcu = <&rcu0>;
85 lantiq,rcu-endian-offset = <0x4c>;
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| /Documentation/filesystems/ |
| D | path-lookup.txt | 22 Since 2.5.62 kernel, dcache has been using a new locking model that uses RCU to
34 Since 2.6.38, RCU is used to make a significant part of the entire path walk
36 even stores into cachelines of common dentries). This is known as "rcu-walk"
84 The hash lists are RCU protected, so list walking is not serialised with
85 concurrent updates (insertion, deletion from the hash). This is a standard RCU
100 Back to the rename case. In usual RCU protected lists, the only operations that
102 list. The object will not be reused until an RCU grace period is complete.
103 This ensures the RCU list traversal primitives can run over the object without
104 problems (see RCU documentation for how this works).
114 new list before waiting for a grace period, this can result in a concurrent RCU
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| /Documentation/litmus-tests/rcu/ |
| D | RCU+sync+read.litmus | 1 C RCU+sync+read
6 * This litmus test demonstrates that after a grace period, an RCU updater always
7 * sees all stores done in prior RCU read-side critical sections. Such
10 * This is one implication of the RCU grace-period guarantee, which says (among
11 * other things) that an RCU read-side critical section cannot span a grace period.
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| D | RCU+sync+free.litmus | 1 C RCU+sync+free
6 * This litmus test demonstrates that an RCU reader can never see a write that
10 * This is a typical pattern of RCU usage, where the write before the grace
14 * This is one implication of the RCU grace-period guarantee, which says (among
15 * other things) that an RCU read-side critical section cannot span a grace period.
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| /Documentation/devicetree/bindings/mips/lantiq/ |
| D | rcu.txt | 1 Lantiq XWAY SoC RCU binding
4 This binding describes the RCU (reset controller unit) multifunction device,
7 The RCU register range is used for multiple purposes. Mostly one device
10 With this patch all accesses to the RCU registers will go through
17 "lantiq,xrx200-rcu", "simple-mfd", "syscon"
22 Example of the RCU bindings on a xRX200 SoC:
23 rcu0: rcu@203000 {
24 compatible = "lantiq,xrx200-rcu", "simple-mfd", "syscon";
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| /Documentation/litmus-tests/ |
| D | README | 70 RCU (/rcu directory)
75 ensure that an RCU reader will not see pre-initialization garbage.
77 RCU+sync+read.litmus
78 RCU+sync+free.litmus
79 Both the above litmus tests demonstrate the RCU grace period guarantee
80 that an RCU read-side critical section can never span a grace period.
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| /Documentation/translations/it_IT/RCU/ |
| D | torture.rst | 6 Le operazioni RCU per le verifiche *torture*
13 RCU. L'opzione creerà un modulo rcutorture che potrete caricare per avviare le
26 …rcu-torture:--- Start of test: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_no_idle_…
27 …rcu-torture: rtc: (null) ver: 155441 tfle: 0 rta: 155441 rtaf: 8884 rtf: 155440 rtmbe: 0…
28 rcu-torture: Reader Pipe: 727860534 34213 0 0 0 0 0 0 0 0 0
29 rcu-torture: Reader Batch: 727877838 17003 0 0 0 0 0 0 0 0 0
30 …rcu-torture: Free-Block Circulation: 155440 155440 155440 155440 155440 155440 155440 155440 1554…
31 …rcu-torture:--- End of test: SUCCESS: nreaders=16 nfakewriters=4 stat_interval=30 verbose=0 test_n…
47 * "ver": Il numero di volte dall'avvio che il processo scrittore di RCU ha
52 illuderti che RCU stia funzionando mentre invece non è il caso. :-/
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| /Documentation/RCU/Design/Data-Structures/ |
| D | Data-Structures.rst | 12 This document describes RCU's major data structures and their relationship
18 RCU is for all intents and purposes a large state machine, and its
19 data structures maintain the state in such a way as to allow RCU readers
20 to execute extremely quickly, while also processing the RCU grace periods
22 The efficiency and scalability of RCU updaters is provided primarily
35 If the actual hardware has only 16 CPUs, RCU will adjust itself
88 32-bit system), then RCU will automatically add more levels to the tree.
90 65,536 CPUs, RCU would configure the ``rcu_node`` tree as follows:
94 RCU currently permits up to a four-level tree, which on a 64-bit system
102 and scalability benefits of partitioning, even though RCU grace-period
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| /Documentation/RCU/Design/Expedited-Grace-Periods/ |
| D | Expedited-Grace-Periods.rst | 8 This document describes RCU's expedited grace periods.
9 Unlike RCU's normal grace periods, which accept long latencies to attain
13 There are two flavors of RCU (RCU-preempt and RCU-sched), with an earlier
14 third RCU-bh flavor having been implemented in terms of the other two.
20 The expedited RCU grace periods cannot be accused of being subtle,
31 As always for RCU, once everything has spent some time in a quiescent
35 operation depend on the RCU flavor, as described in the following
38 RCU-preempt Expedited Grace Periods
41 ``CONFIG_PREEMPTION=y`` kernels implement RCU-preempt.
42 The overall flow of the handling of a given CPU by an RCU-preempt
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| /Documentation/devicetree/bindings/reset/ |
| D | intel,rcu-gw.yaml | 4 $id: http://devicetree.org/schemas/reset/intel,rcu-gw.yaml#
15 - intel,rcu-lgm
16 - intel,rcu-xrx200
53 compatible = "intel,rcu-lgm";
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| /Documentation/core-api/ |
| D | entry.rst | 9 * RCU / Context tracking
21 Most instrumentation facilities depend on RCU, so instrumentation is prohibited
22 for entry code before RCU starts watching and exit code after RCU stops
55 All non-instrumentable entry/exit code sections before and after the RCU
85 * RCU / Context tracking
99 * RCU / Context tracking
108 Do not nest syscalls. Nested systcalls will cause RCU and/or context tracking
138 exit handling is slightly different. RCU state is only updated when the
139 interrupt is raised in the context of the CPU's idle task. Otherwise, RCU will
217 * RCU / Context tracking
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