diff options
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/RTFP.txt | 77 | ||||
| -rw-r--r-- | Documentation/RCU/UP.txt | 34 | ||||
| -rw-r--r-- | Documentation/RCU/checklist.txt | 20 | ||||
| -rw-r--r-- | Documentation/RCU/rcu.txt | 10 | ||||
| -rw-r--r-- | Documentation/RCU/rcubarrier.txt | 7 | ||||
| -rw-r--r-- | Documentation/RCU/rculist_nulls.txt | 7 | ||||
| -rw-r--r-- | Documentation/RCU/torture.txt | 23 | ||||
| -rw-r--r-- | Documentation/RCU/trace.txt | 7 | ||||
| -rw-r--r-- | Documentation/RCU/whatisRCU.txt | 22 |
9 files changed, 174 insertions, 33 deletions
diff --git a/Documentation/RCU/RTFP.txt b/Documentation/RCU/RTFP.txt index 9f711d2df91b..d2b85237c76e 100644 --- a/Documentation/RCU/RTFP.txt +++ b/Documentation/RCU/RTFP.txt @@ -743,3 +743,80 @@ Revised: RCU, realtime RCU, sleepable RCU, performance. " } + +@article{PaulEMcKenney2008RCUOSR +,author="Paul E. McKenney and Jonathan Walpole" +,title="Introducing technology into the {Linux} kernel: a case study" +,Year="2008" +,journal="SIGOPS Oper. Syst. Rev." +,volume="42" +,number="5" +,pages="4--17" +,issn="0163-5980" +,doi={http://doi.acm.org/10.1145/1400097.1400099} +,publisher="ACM" +,address="New York, NY, USA" +,annotation={ + Linux changed RCU to a far greater degree than RCU has changed Linux. +} +} + +@unpublished{PaulEMcKenney2008HierarchicalRCU +,Author="Paul E. McKenney" +,Title="Hierarchical {RCU}" +,month="November" +,day="3" +,year="2008" +,note="Available: +\url{http://lwn.net/Articles/305782/} +[Viewed November 6, 2008]" +,annotation=" + RCU with combining-tree-based grace-period detection, + permitting it to handle thousands of CPUs. +" +} + +@conference{PaulEMcKenney2009MaliciousURCU +,Author="Paul E. McKenney" +,Title="Using a Malicious User-Level {RCU} to Torture {RCU}-Based Algorithms" +,Booktitle="linux.conf.au 2009" +,month="January" +,year="2009" +,address="Hobart, Australia" +,note="Available: +\url{http://www.rdrop.com/users/paulmck/RCU/urcutorture.2009.01.22a.pdf} +[Viewed February 2, 2009]" +,annotation=" + Realtime RCU and torture-testing RCU uses. +" +} + +@unpublished{MathieuDesnoyers2009URCU +,Author="Mathieu Desnoyers" +,Title="[{RFC} git tree] Userspace {RCU} (urcu) for {Linux}" +,month="February" +,day="5" +,year="2009" +,note="Available: +\url{http://lkml.org/lkml/2009/2/5/572} +\url{git://lttng.org/userspace-rcu.git} +[Viewed February 20, 2009]" +,annotation=" + Mathieu Desnoyers's user-space RCU implementation. + git://lttng.org/userspace-rcu.git +" +} + +@unpublished{PaulEMcKenney2009BloatWatchRCU +,Author="Paul E. McKenney" +,Title="{RCU}: The {Bloatwatch} Edition" +,month="March" +,day="17" +,year="2009" +,note="Available: +\url{http://lwn.net/Articles/323929/} +[Viewed March 20, 2009]" +,annotation=" + Uniprocessor assumptions allow simplified RCU implementation. +" +} diff --git a/Documentation/RCU/UP.txt b/Documentation/RCU/UP.txt index aab4a9ec3931..90ec5341ee98 100644 --- a/Documentation/RCU/UP.txt +++ b/Documentation/RCU/UP.txt @@ -2,14 +2,13 @@ RCU on Uniprocessor Systems A common misconception is that, on UP systems, the call_rcu() primitive -may immediately invoke its function, and that the synchronize_rcu() -primitive may return immediately. The basis of this misconception +may immediately invoke its function. The basis of this misconception is that since there is only one CPU, it should not be necessary to wait for anything else to get done, since there are no other CPUs for anything else to be happening on. Although this approach will -sort- -of- work a surprising amount of the time, it is a very bad idea in general. -This document presents three examples that demonstrate exactly how bad an -idea this is. +This document presents three examples that demonstrate exactly how bad +an idea this is. Example 1: softirq Suicide @@ -82,11 +81,18 @@ Quick Quiz #2: What locking restriction must RCU callbacks respect? Summary -Permitting call_rcu() to immediately invoke its arguments or permitting -synchronize_rcu() to immediately return breaks RCU, even on a UP system. -So do not do it! Even on a UP system, the RCU infrastructure -must- -respect grace periods, and -must- invoke callbacks from a known environment -in which no locks are held. +Permitting call_rcu() to immediately invoke its arguments breaks RCU, +even on a UP system. So do not do it! Even on a UP system, the RCU +infrastructure -must- respect grace periods, and -must- invoke callbacks +from a known environment in which no locks are held. + +It -is- safe for synchronize_sched() and synchronize_rcu_bh() to return +immediately on an UP system. It is also safe for synchronize_rcu() +to return immediately on UP systems, except when running preemptable +RCU. + +Quick Quiz #3: Why can't synchronize_rcu() return immediately on + UP systems running preemptable RCU? Answer to Quick Quiz #1: @@ -117,3 +123,13 @@ Answer to Quick Quiz #2: callbacks acquire locks directly. However, a great many RCU callbacks do acquire locks -indirectly-, for example, via the kfree() primitive. + +Answer to Quick Quiz #3: + Why can't synchronize_rcu() return immediately on UP systems + running preemptable RCU? + + Because some other task might have been preempted in the middle + of an RCU read-side critical section. If synchronize_rcu() + simply immediately returned, it would prematurely signal the + end of the grace period, which would come as a nasty shock to + that other thread when it started running again. diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index accfe2f5247d..51525a30e8b4 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -11,7 +11,10 @@ over a rather long period of time, but improvements are always welcome! structure is updated more than about 10% of the time, then you should strongly consider some other approach, unless detailed performance measurements show that RCU is nonetheless - the right tool for the job. + the right tool for the job. Yes, you might think of RCU + as simply cutting overhead off of the readers and imposing it + on the writers. That is exactly why normal uses of RCU will + do much more reading than updating. Another exception is where performance is not an issue, and RCU provides a simpler implementation. An example of this situation @@ -240,10 +243,11 @@ over a rather long period of time, but improvements are always welcome! instead need to use synchronize_irq() or synchronize_sched(). 12. Any lock acquired by an RCU callback must be acquired elsewhere - with irq disabled, e.g., via spin_lock_irqsave(). Failing to - disable irq on a given acquisition of that lock will result in - deadlock as soon as the RCU callback happens to interrupt that - acquisition's critical section. + with softirq disabled, e.g., via spin_lock_irqsave(), + spin_lock_bh(), etc. Failing to disable irq on a given + acquisition of that lock will result in deadlock as soon as the + RCU callback happens to interrupt that acquisition's critical + section. 13. RCU callbacks can be and are executed in parallel. In many cases, the callback code simply wrappers around kfree(), so that this @@ -310,3 +314,9 @@ over a rather long period of time, but improvements are always welcome! Because these primitives only wait for pre-existing readers, it is the caller's responsibility to guarantee safety to any subsequent readers. + +16. The various RCU read-side primitives do -not- contain memory + barriers. The CPU (and in some cases, the compiler) is free + to reorder code into and out of RCU read-side critical sections. + It is the responsibility of the RCU update-side primitives to + deal with this. diff --git a/Documentation/RCU/rcu.txt b/Documentation/RCU/rcu.txt index 7aa2002ade77..2a23523ce471 100644 --- a/Documentation/RCU/rcu.txt +++ b/Documentation/RCU/rcu.txt @@ -36,7 +36,7 @@ o How can the updater tell when a grace period has completed executed in user mode, or executed in the idle loop, we can safely free up that item. - Preemptible variants of RCU (CONFIG_PREEMPT_RCU) get the + Preemptible variants of RCU (CONFIG_TREE_PREEMPT_RCU) get the same effect, but require that the readers manipulate CPU-local counters. These counters allow limited types of blocking within RCU read-side critical sections. SRCU also uses @@ -79,10 +79,10 @@ o I hear that RCU is patented? What is with that? o I hear that RCU needs work in order to support realtime kernels? This work is largely completed. Realtime-friendly RCU can be - enabled via the CONFIG_PREEMPT_RCU kernel configuration parameter. - However, work is in progress for enabling priority boosting of - preempted RCU read-side critical sections. This is needed if you - have CPU-bound realtime threads. + enabled via the CONFIG_TREE_PREEMPT_RCU kernel configuration + parameter. However, work is in progress for enabling priority + boosting of preempted RCU read-side critical sections. This is + needed if you have CPU-bound realtime threads. o Where can I find more information on RCU? diff --git a/Documentation/RCU/rcubarrier.txt b/Documentation/RCU/rcubarrier.txt index 909602d409bb..e439a0edee22 100644 --- a/Documentation/RCU/rcubarrier.txt +++ b/Documentation/RCU/rcubarrier.txt @@ -170,6 +170,13 @@ module invokes call_rcu() from timers, you will need to first cancel all the timers, and only then invoke rcu_barrier() to wait for any remaining RCU callbacks to complete. +Of course, if you module uses call_rcu_bh(), you will need to invoke +rcu_barrier_bh() before unloading. Similarly, if your module uses +call_rcu_sched(), you will need to invoke rcu_barrier_sched() before +unloading. If your module uses call_rcu(), call_rcu_bh(), -and- +call_rcu_sched(), then you will need to invoke each of rcu_barrier(), +rcu_barrier_bh(), and rcu_barrier_sched(). + Implementing rcu_barrier() diff --git a/Documentation/RCU/rculist_nulls.txt b/Documentation/RCU/rculist_nulls.txt index 93cb28d05dcd..18f9651ff23d 100644 --- a/Documentation/RCU/rculist_nulls.txt +++ b/Documentation/RCU/rculist_nulls.txt @@ -83,11 +83,12 @@ not detect it missed following items in original chain. obj = kmem_cache_alloc(...); lock_chain(); // typically a spin_lock() obj->key = key; -atomic_inc(&obj->refcnt); /* * we need to make sure obj->key is updated before obj->next + * or obj->refcnt */ smp_wmb(); +atomic_set(&obj->refcnt, 1); hlist_add_head_rcu(&obj->obj_node, list); unlock_chain(); // typically a spin_unlock() @@ -159,6 +160,10 @@ out: obj = kmem_cache_alloc(cachep); lock_chain(); // typically a spin_lock() obj->key = key; +/* + * changes to obj->key must be visible before refcnt one + */ +smp_wmb(); atomic_set(&obj->refcnt, 1); /* * insert obj in RCU way (readers might be traversing chain) diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt index a342b6e1cc10..9dba3bb90e60 100644 --- a/Documentation/RCU/torture.txt +++ b/Documentation/RCU/torture.txt @@ -76,8 +76,10 @@ torture_type The type of RCU to test: "rcu" for the rcu_read_lock() API, "rcu_sync" for rcu_read_lock() with synchronous reclamation, "rcu_bh" for the rcu_read_lock_bh() API, "rcu_bh_sync" for rcu_read_lock_bh() with synchronous reclamation, "srcu" for - the "srcu_read_lock()" API, and "sched" for the use of - preempt_disable() together with synchronize_sched(). + the "srcu_read_lock()" API, "sched" for the use of + preempt_disable() together with synchronize_sched(), + and "sched_expedited" for the use of preempt_disable() + with synchronize_sched_expedited(). verbose Enable debug printk()s. Default is disabled. @@ -162,6 +164,23 @@ of the "old" and "current" counters for the corresponding CPU. The "idx" value maps the "old" and "current" values to the underlying array, and is useful for debugging. +Similarly, sched_expedited RCU provides the following: + + sched_expedited-torture: rtc: d0000000016c1880 ver: 1090796 tfle: 0 rta: 1090796 rtaf: 0 rtf: 1090787 rtmbe: 0 nt: 27713319 + sched_expedited-torture: Reader Pipe: 12660320201 95875 0 0 0 0 0 0 0 0 0 + sched_expedited-torture: Reader Batch: 12660424885 0 0 0 0 0 0 0 0 0 0 + sched_expedited-torture: Free-Block Circulation: 1090795 1090795 1090794 1090793 1090792 1090791 1090790 1090789 1090788 1090787 0 + state: -1 / 0:0 3:0 4:0 + +As before, the first four lines are similar to those for RCU. +The last line shows the task-migration state. The first number is +-1 if synchronize_sched_expedited() is idle, -2 if in the process of +posting wakeups to the migration kthreads, and N when waiting on CPU N. +Each of the colon-separated fields following the "/" is a CPU:state pair. +Valid states are "0" for idle, "1" for waiting for quiescent state, +"2" for passed through quiescent state, and "3" when a race with a +CPU-hotplug event forces use of the synchronize_sched() primitive. + USAGE diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index 02cced183b2d..187bbf10c923 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -191,8 +191,7 @@ rcu/rcuhier (which displays the struct rcu_node hierarchy). The output of "cat rcu/rcudata" looks as follows: -rcu: -rcu: +rcu_sched: 0 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=10951/1 dn=0 df=1101 of=0 ri=36 ql=0 b=10 1 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=16117/1 dn=0 df=1015 of=0 ri=0 ql=0 b=10 2 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1445/1 dn=0 df=1839 of=0 ri=0 ql=0 b=10 @@ -306,7 +305,7 @@ comma-separated-variable spreadsheet format. The output of "cat rcu/rcugp" looks as follows: -rcu: completed=33062 gpnum=33063 +rcu_sched: completed=33062 gpnum=33063 rcu_bh: completed=464 gpnum=464 Again, this output is for both "rcu" and "rcu_bh". The fields are @@ -413,7 +412,7 @@ o Each element of the form "1/1 0:127 ^0" represents one struct The output of "cat rcu/rcu_pending" looks as follows: -rcu: +rcu_sched: 0 np=255892 qsp=53936 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741 1 np=261224 qsp=54638 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792 2 np=237496 qsp=49664 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629 diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 96170824a717..e41a7fecf0d3 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -136,10 +136,10 @@ rcu_read_lock() Used by a reader to inform the reclaimer that the reader is entering an RCU read-side critical section. It is illegal to block while in an RCU read-side critical section, though - kernels built with CONFIG_PREEMPT_RCU can preempt RCU read-side - critical sections. Any RCU-protected data structure accessed - during an RCU read-side critical section is guaranteed to remain - unreclaimed for the full duration of that critical section. + kernels built with CONFIG_TREE_PREEMPT_RCU can preempt RCU + read-side critical sections. Any RCU-protected data structure + accessed during an RCU read-side critical section is guaranteed to + remain unreclaimed for the full duration of that critical section. Reference counts may be used in conjunction with RCU to maintain longer-term references to data structures. @@ -785,6 +785,7 @@ RCU pointer/list traversal: rcu_dereference list_for_each_entry_rcu hlist_for_each_entry_rcu + hlist_nulls_for_each_entry_rcu list_for_each_continue_rcu (to be deprecated in favor of new list_for_each_entry_continue_rcu) @@ -807,19 +808,23 @@ RCU: Critical sections Grace period Barrier rcu_read_lock synchronize_net rcu_barrier rcu_read_unlock synchronize_rcu + synchronize_rcu_expedited call_rcu bh: Critical sections Grace period Barrier rcu_read_lock_bh call_rcu_bh rcu_barrier_bh - rcu_read_unlock_bh + rcu_read_unlock_bh synchronize_rcu_bh + synchronize_rcu_bh_expedited sched: Critical sections Grace period Barrier - [preempt_disable] synchronize_sched rcu_barrier_sched - [and friends] call_rcu_sched + rcu_read_lock_sched synchronize_sched rcu_barrier_sched + rcu_read_unlock_sched call_rcu_sched + [preempt_disable] synchronize_sched_expedited + [and friends] SRCU: Critical sections Grace period Barrier @@ -827,6 +832,9 @@ SRCU: Critical sections Grace period Barrier srcu_read_lock synchronize_srcu N/A srcu_read_unlock +SRCU: Initialization/cleanup + init_srcu_struct + cleanup_srcu_struct See the comment headers in the source code (or the docbook generated from them) for more information. |