Real-Time Preemption, -RT-2.6.13-rc4-V0.7.52-01]

diff -urpN -X dontdiff linux-2.6.13-rc4/Documentation/RCU/proc.txt linux-2.6.13-rc4-IngoRTRCU/Documentation/RCU/proc.txt
@@ -0,0 +1,207 @@
+/proc Filesystem Entries for RCU
+
+
+CONFIG_RCU_STATS
+
+The CONFIG_RCU_STATS config option is available only in conjunction with
+CONFIG_PREEMPT_RCU.  It makes four /proc entries available, namely: rcuctrs,
+rcuptrs, rcugp, and rcustats.
+
+/proc/rcuctrs
+
+	CPU last cur
+	  0    1   1
+	  1    1   1
+	  2    1   1
+	  3    0   2
+	ggp = 230725
+
+This displays the number of processes that started RCU read-side critical
+sections on each CPU.  In absence of preemption, the "last" and "cur"
+counts for a given CPU will always sum to one.  Therefore, in the example
+output above, each CPU has started one RCU read-side critical section
+that was later preempted.  The "last" column counts RCU read-side critical
+sections that started prior to the last counter flip, while the "cur"
+column counts critical sections that started after the last counter flip.
+
+The "ggp" count is a count of the number of counter flips since boot.
+Since this is shown as an odd number, the "cur" counts are stored in
+the zero-th element of each of the per-CPU arrays, and the "last" counts
+are stored in the first element of each of the per-CPU arrays.
+
+
+/proc/rcuptrs
+
+	nl=c04c7160/c04c7960 nt=c04c72d0
+	 wl=c04c7168/c04c794c wt=c04c72bc dl=c04c7170/00000000 dt=c04c7170
+
+This displays the head and tail of each of CONFIG_PREEMPT_RCU's three
+callback lists.  This will soon change to display this on a per-CPU
+basis, since each CPU will soon have its own set of callback lists.
+In the example above, the "next" list header is located at hex address
+0xc04c7160, the first element on the list at hex address 0xc04c7960,
+and the last element on the list at hex address 0xc04c72d0.  The "wl="
+and "wt=" output is similar for the "wait" list, and the "dl=" and "dt="
+output for the "done" list.  The "done" list is normally emptied very
+quickly after being filled, so will usually be empty as shown above.
+Note that the tail pointer points into the list header in this case.
+
+Callbacks are placed in the "next" list by call_rcu(), moved to the
+"wait" list after the next counter flip, and moved to the "done" list
+on the counter flip after that.  Once on the "done" list, the callbacks
+are invoked.
+
+
+/proc/rcugp
+
+	oldggp=241419  newggp=241421
+
+This entry invokes synchronize_rcu() and prints out the number of counter
+flips since boot before and after the synchronize_rcu().  These two
+numbers will always differ by at least two.  Unless RCU is broken.  ;-)
+
+
+/proc/rcustats
+
+	ggp=242416 lgp=242416 sr=0 rcc=396233
+	na=2090938 nl=9 wa=2090929 wl=9 dl=0 dr=2090920 di=2090920
+	rtf1=22230730 rtf2=20139162 rtf3=242416 rtfe1=2085911 rtfe2=5657 rtfe3=19896746
+
+The quantities printed are as follows:
+
+o	"ggp=": The number of flips since boot.
+
+o	"lgp=": The number of flips sensed by the local structure since
+	boot.  This will soon be per-CPU.
+
+o	"sr=": The number of explicit call to synchronize_rcu().
+	Except that this is currently broken, so always reads as zero.
+	It is likely to be removed...
+
+o	"rcc=": The number of calls to rcu_check_callbacks().
+
+o	"na=": The number of callbacks that call_rcu() has registered
+	since boot.
+
+o	"nl=": The number of callbacks currently on the "next" list.
+
+o	"wa=": The number of callbacks that have moved to the "wait"
+	list since boot.
+
+o	"wl=": The number of callbacks currently on the "wait" list.
+
+o	"da=": The number of callbacks that have been moved to the
+	"done" list since boot.
+
+o	"dl=": The number of callbacks currently on the "done" list.
+
+o	"dr=": The number of callbacks that have been removed from the
+	"done" list since boot.
+
+o	"di=": The number of callbacks that have been invoked after being
+	removed from the "done" list.
+
+o	"rtf1=": The number of attempts to flip the counters.
+
+o	"rtf2=": The number of attempts to flip the counters that successfully
+	acquired the fliplock.
+
+o	"rtf3=": The number of successful counter flips.
+
+o	"rtfe1=": The number of attempts to flip the counters that failed
+	due to the lock being held by someone else.
+
+o	"rtfe2=": The number of attempts to flip the counters that were
+	abandoned due to someone else doing the job for us.
+
+o	"rtfe3=": The number of attempts to flip the counters that failed
+	due to some task still being in an RCU read-side critical section
+	starting from before the last successful counter flip.
+
+
+CONFIG_RCU_TORTURE_TEST
+
+The CONFIG_RCU_TORTURE_TEST config option is available for all RCU
+implementations.  It makes three /proc entries available, namely: rcutw,
+rcutr, and rcuts.
+
+
+/proc/rcutw
+
+Reading this entry starts a new torture test, or ends an earlier one
+if one is already in progress (in other words, there can be only one
+writer at a time).  This sleeps uninterruptibly, so be sure to run
+it in the background.  One could argue that it would be good to have
+multiple writers, but Linux uses RCU heavily enough that you will get
+write-side contention whether you want it or not.  If you want additional
+write-side contention, repeatedly create and destroy several large file
+trees in parallel.  Or use some other RCU-protected update.
+
+
+/proc/rcutr
+
+Reading this entry starts a new torture reader, which runs until sent
+a signal (e.g., control-C).  If testing an RCU implementation with
+preemptible read-side critical sections, make sure to spawn at least
+two /proc/rcutr instances for each CPU.
+
+
+/proc/rcuts
+
+Displays the current state of the torture test:
+
+	ggp = 20961
+	rtc: c04496f4 ver: 8734 tfle: 0 rta: 8734 rtaf: 0 rtf: 8715
+	Reader Pipe:  88024120 63914 0 0 0 0 0 0 0 0 0
+	Reader Batch:  88024097 63937 0 0 0 0 0 0 0 0
+	Free-Block Circulation:  8733 8731 8729 8727 8725 8723 8721 8719 8717 8715 0
+
+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.
+
+o	"ver": The number of times since boot that the rcutw writer task
+	has changed the structure visible to readers.
+
+o	"tfle": If non-zero, indicates that the "torture freelist"
+	containing structure to be placed into the "rtc" area is empty.
+	This condition is important, since it can fool you into thinking
+	that RCU is working when it is not.  :-/
+
+o	"rta": Number of structures allocated from the torture freelist.
+
+o	"rtaf": Number of allocations from the torture freelist that have
+	failed due to the list being empty.
+	
+o	"rtf": Number of frees into the torture freelist.
+
+o	"Reader Pipe": Histogram of "ages" of structures seen by readers.
+	If any entries past the first two are non-zero, RCU is broken.
+	And /proc/rcuts prints "!!!" to make sure you notice.  The age
+	of a newly allocated structure is zero, it becomes one when
+	removed from reader visibility, and is incremented once per
+	grace period subsequently -- and is freed after passing through
+	(RCU_TORTURE_PIPE_LEN-2) grace periods.
+
+	The output displayed above was taken from a correctly working
+	RCU.  If you want to see what it looks like when broken, break
+	it yourself.  ;-)
+
+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
+	"Reader Batch" list than in the "Reader Pipe" list.
+
+o	"Free-Block Circulation": Shows the number of torture structures
+	that have reached a given point in the pipeline.  The first element
+	should closely correspond to the number of structures allocated,
+	the second to the number that have been removed from reader view,
+	and all but the last remaining to the corresponding number of
+	passes through a grace period.  The last entry should be zero,
+	as it is only incremented if a torture structure's counter
+	somehow gets incremented farther than it should.

diff -urpN -X dontdiff linux-2.6.13-rc4/kernel/Kconfig.preempt linux-2.6.13-rc4-IngoRTRCU/kernel/Kconfig.preempt
@@ -63,3 +63,38 @@ config PREEMPT_BKL
 	  Say Y here if you are building a kernel for a desktop system.
 	  Say N if you are unsure.
 
+config PREEMPT_RCU
+	bool "Preemptible RCU"
+	default n
+	depends on PREEMPT
+	help
+	  This option reduces the latency of the kernel by making certain
+	  RCU sections preemptible. Normally RCU code is non-preemptible, if
+	  this option is selected then read-only RCU sections become
+	  preemptible. This helps latency, but may expose bugs due to
+	  now-naive assumptions about each RCU read-side critical section
+	  remaining on a given CPU through its execution.
+
+	  Say N if you are unsure.
+
+config RCU_STATS
+	bool "/proc stats for preemptible RCU read-side critical sections"
+	depends on PREEMPT_RCU
+	default y
+	help
+	  This option provides /proc stats to provide debugging info for
+	  the preemptible realtime RCU implementation.
+
+	  Say Y here if you want to see RCU stats in /proc
+	  Say N if you are unsure.
+
+config RCU_TORTURE_TEST
+	bool "/proc torture tests for RCU"
+	default y
+	help
+	  This option provides /proc files that run torture tests on
+	  the preemptible realtime RCU implementation.
+
+	  Say Y here if you want to be able to run RCU torture tests.
+	  Say N if you are unsure.
+