cfq-iosched: fix RCU race in the cfq io_context destructor handling

[linux-2.6-omap-h63xx.git] / Documentation / RCU / torture.txt

diff --git a/Documentation/RCU/torture.txt b/Documentation/RCU/torture.txt
index a4948591607d0e1d7b653ce1f66c08e4831cbad1..2967a65269d8af7702dbe76f4780e14d91dd9061 100644 (file)
--- a/Documentation/RCU/torture.txt
+++ b/Documentation/RCU/torture.txt
@@ -28,6 +28,15 @@ nreaders     This is the number of RCU reading threads supported.
                To properly exercise RCU implementations with preemptible
                read-side critical sections.
 
+nfakewriters   This is the number of RCU fake writer threads to run.  Fake
+               writer threads repeatedly use the synchronous "wait for
+               current readers" function of the interface selected by
+               torture_type, with a delay between calls to allow for various
+               different numbers of writers running in parallel.
+               nfakewriters defaults to 4, which provides enough parallelism
+               to trigger special cases caused by multiple writers, such as
+               the synchronize_srcu() early return optimization.
+
 stat_interval  The number of seconds between output of torture
                statistics (via printk()).  Regardless of the interval,
                statistics are printed when the module is unloaded.
@@ -37,16 +46,20 @@ stat_interval       The number of seconds between output of torture
 
 shuffle_interval
                The number of seconds to keep the test threads affinitied
-               to a particular subset of the CPUs.  Used in conjunction
-               with test_no_idle_hz.
+               to a particular subset of the CPUs, defaults to 5 seconds.
+               Used in conjunction with test_no_idle_hz.
 
 test_no_idle_hz        Whether or not to test the ability of RCU to operate in
                a kernel that disables the scheduling-clock interrupt to
                idle CPUs.  Boolean parameter, "1" to test, "0" otherwise.
+               Defaults to omitting this test.
 
-torture_type   The type of RCU to test: "rcu" for the rcu_read_lock()
-               API, "rcu_bh" for the rcu_read_lock_bh() API, and "srcu"
-               for the "srcu_read_lock()" API.
+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().
 
 verbose                Enable debug printk()s.  Default is disabled.
 
@@ -70,8 +83,6 @@ be evident.  ;-)
 
 The entries are as follows:
 
-o      "ggp": The number of counter flips (or batches) since boot.
-
 o      "rtc": The hexadecimal address of the structure currently visible
        to readers.
 
@@ -105,8 +116,8 @@ o   "Reader Pipe": Histogram of "ages" of structures seen by readers.
 o      "Reader Batch": Another histogram of "ages" of structures seen
        by readers, but in terms of counter flips (or batches) rather
        than in terms of grace periods.  The legal number of non-zero
-       entries is again two.  The reason for this separate view is
-       that it is easier to get the third entry to show up in the
+       entries is again two.  The reason for this separate view is that
+       it is sometimes easier to get the third entry to show up in the
        "Reader Batch" list than in the "Reader Pipe" list.
 
 o      "Free-Block Circulation": Shows the number of torture structures
@@ -118,6 +129,21 @@ o  "Free-Block Circulation": Shows the number of torture structures
        as it is only incremented if a torture structure's counter
        somehow gets incremented farther than it should.
 
+Different implementations of RCU can provide implementation-specific
+additional information.  For example, SRCU provides the following:
+
+       srcu-torture: rtc: f8cf46a8 ver: 355 tfle: 0 rta: 356 rtaf: 0 rtf: 346 rtmbe: 0
+       srcu-torture: Reader Pipe:  559738 939 0 0 0 0 0 0 0 0 0
+       srcu-torture: Reader Batch:  560434 243 0 0 0 0 0 0 0 0
+       srcu-torture: Free-Block Circulation:  355 354 353 352 351 350 349 348 347 346 0
+       srcu-torture: per-CPU(idx=1): 0(0,1) 1(0,1) 2(0,0) 3(0,1)
+
+The first four lines are similar to those for RCU.  The last line shows
+the per-CPU counter state.  The numbers in parentheses are the values
+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.
+
 
 USAGE