Merge branch 'linus' into x86/cleanups

Description:

                Write:

                <channel> [<bpst offset>]

                <channel>

                to start beaconing on a specific channel, or stop

                beaconing if <channel> is -1.  Valid channels depends

                on the radio controller's supported band groups.

                to force a specific channel to be used when beaconing,

                or, if <channel> is -1, to prohibit beaconing.  If

                <channel> is 0, then the default channel selection

                algorithm will be used.  Valid channels depends on the

                radio controller's supported band groups.

                <bpst offset> may be used to try and join a specific

                beacon group if more than one was found during a scan.

                Reading returns the currently active channel, or -1 if

                the radio controller is not beaconing.

What:           /sys/class/uwb_rc/uwbN/scan

Date:           July 2008

	- List of RCU papers (bibliography) going back to 1980.

torture.txt

	- RCU Torture Test Operation (CONFIG_RCU_TORTURE_TEST)

trace.txt

	- CONFIG_RCU_TRACE debugfs files and formats

UP.txt

	- RCU on Uniprocessor Systems

whatisRCU.txt

CONFIG_RCU_TRACE debugfs Files and Formats

The rcupreempt and rcutree implementations of RCU provide debugfs trace

output that summarizes counters and state.  This information is useful for

debugging RCU itself, and can sometimes also help to debug abuses of RCU.

Note that the rcuclassic implementation of RCU does not provide debugfs

trace output.

The following sections describe the debugfs files and formats for

preemptable RCU (rcupreempt) and hierarchical RCU (rcutree).

Preemptable RCU debugfs Files and Formats

This implementation of RCU provides three debugfs files under the

top-level directory RCU: rcu/rcuctrs (which displays the per-CPU

counters used by preemptable RCU) rcu/rcugp (which displays grace-period

counters), and rcu/rcustats (which internal counters for debugging RCU).

The output of "cat rcu/rcuctrs" looks as follows:

CPU last cur F M

  0    5  -5 0 0

  1   -1   0 0 0

  2    0   1 0 0

  3    0   1 0 0

  4    0   1 0 0

  5    0   1 0 0

  6    0   2 0 0

  7    0  -1 0 0

  8    0   1 0 0

ggp = 26226, state = waitzero

The per-CPU fields are as follows:

o	"CPU" gives the CPU number.  Offline CPUs are not displayed.

o	"last" gives the value of the counter that is being decremented

	for the current grace period phase.  In the example above,

	the counters sum to 4, indicating that there are still four

	RCU read-side critical sections still running that started

	before the last counter flip.

o	"cur" gives the value of the counter that is currently being

	both incremented (by rcu_read_lock()) and decremented (by

	rcu_read_unlock()).  In the example above, the counters sum to

	1, indicating that there is only one RCU read-side critical section

	still running that started after the last counter flip.

o	"F" indicates whether RCU is waiting for this CPU to acknowledge

	a counter flip.  In the above example, RCU is not waiting on any,

	which is consistent with the state being "waitzero" rather than

	"waitack".

o	"M" indicates whether RCU is waiting for this CPU to execute a

	memory barrier.  In the above example, RCU is not waiting on any,

	which is consistent with the state being "waitzero" rather than

	"waitmb".

o	"ggp" is the global grace-period counter.

o	"state" is the RCU state, which can be one of the following:

	o	"idle": there is no grace period in progress.

	o	"waitack": RCU just incremented the global grace-period

		counter, which has the effect of reversing the roles of

		the "last" and "cur" counters above, and is waiting for

		all the CPUs to acknowledge the flip.  Once the flip has

		been acknowledged, CPUs will no longer be incrementing

		what are now the "last" counters, so that their sum will

		decrease monotonically down to zero.

	o	"waitzero": RCU is waiting for the sum of the "last" counters

		to decrease to zero.

	o	"waitmb": RCU is waiting for each CPU to execute a memory

		barrier, which ensures that instructions from a given CPU's

		last RCU read-side critical section cannot be reordered

		with instructions following the memory-barrier instruction.

The output of "cat rcu/rcugp" looks as follows:

oldggp=48870  newggp=48873

Note that reading from this file provokes a synchronize_rcu().  The

"oldggp" value is that of "ggp" from rcu/rcuctrs above, taken before

executing the synchronize_rcu(), and the "newggp" value is also the

"ggp" value, but taken after the synchronize_rcu() command returns.

The output of "cat rcu/rcugp" looks as follows:

na=1337955 nl=40 wa=1337915 wl=44 da=1337871 dl=0 dr=1337871 di=1337871

1=50989 e1=6138 i1=49722 ie1=82 g1=49640 a1=315203 ae1=265563 a2=49640

z1=1401244 ze1=1351605 z2=49639 m1=5661253 me1=5611614 m2=49639

These are counters tracking internal preemptable-RCU events, however,

some of them may be useful for debugging algorithms using RCU.  In

particular, the "nl", "wl", and "dl" values track the number of RCU

callbacks in various states.  The fields are as follows:

o	"na" is the total number of RCU callbacks that have been enqueued

	since boot.

o	"nl" is the number of RCU callbacks waiting for the previous

	grace period to end so that they can start waiting on the next

	grace period.

o	"wa" is the total number of RCU callbacks that have started waiting

	for a grace period since boot.  "na" should be roughly equal to

	"nl" plus "wa".

o	"wl" is the number of RCU callbacks currently waiting for their

	grace period to end.

o	"da" is the total number of RCU callbacks whose grace periods

	have completed since boot.  "wa" should be roughly equal to

	"wl" plus "da".

o	"dr" is the total number of RCU callbacks that have been removed

	from the list of callbacks ready to invoke.  "dr" should be roughly

	equal to "da".

o	"di" is the total number of RCU callbacks that have been invoked

	since boot.  "di" should be roughly equal to "da", though some

	early versions of preemptable RCU had a bug so that only the

	last CPU's count of invocations was displayed, rather than the

	sum of all CPU's counts.

o	"1" is the number of calls to rcu_try_flip().  This should be

	roughly equal to the sum of "e1", "i1", "a1", "z1", and "m1"

	described below.  In other words, the number of times that

	the state machine is visited should be equal to the sum of the

	number of times that each state is visited plus the number of

	times that the state-machine lock acquisition failed.

o	"e1" is the number of times that rcu_try_flip() was unable to

	acquire the fliplock.

o	"i1" is the number of calls to rcu_try_flip_idle().

o	"ie1" is the number of times rcu_try_flip_idle() exited early

	due to the calling CPU having no work for RCU.

o	"g1" is the number of times that rcu_try_flip_idle() decided

	to start a new grace period.  "i1" should be roughly equal to

	"ie1" plus "g1".

o	"a1" is the number of calls to rcu_try_flip_waitack().

o	"ae1" is the number of times that rcu_try_flip_waitack() found

	that at least one CPU had not yet acknowledge the new grace period

	(AKA "counter flip").

o	"a2" is the number of time rcu_try_flip_waitack() found that

	all CPUs had acknowledged.  "a1" should be roughly equal to

	"ae1" plus "a2".  (This particular output was collected on

	a 128-CPU machine, hence the smaller-than-usual fraction of

	calls to rcu_try_flip_waitack() finding all CPUs having already

	acknowledged.)

o	"z1" is the number of calls to rcu_try_flip_waitzero().

o	"ze1" is the number of times that rcu_try_flip_waitzero() found

	that not all of the old RCU read-side critical sections had

	completed.

o	"z2" is the number of times that rcu_try_flip_waitzero() finds

	the sum of the counters equal to zero, in other words, that

	all of the old RCU read-side critical sections had completed.

	The value of "z1" should be roughly equal to "ze1" plus

	"z2".

o	"m1" is the number of calls to rcu_try_flip_waitmb().

o	"me1" is the number of times that rcu_try_flip_waitmb() finds

	that at least one CPU has not yet executed a memory barrier.

o	"m2" is the number of times that rcu_try_flip_waitmb() finds that

	all CPUs have executed a memory barrier.

Hierarchical RCU debugfs Files and Formats

This implementation of RCU provides three debugfs files under the

top-level directory RCU: rcu/rcudata (which displays fields in struct

rcu_data), rcu/rcugp (which displays grace-period counters), and

rcu/rcuhier (which displays the struct rcu_node hierarchy).

The output of "cat rcu/rcudata" looks as follows:

rcu:

  0 c=4011 g=4012 pq=1 pqc=4011 qp=0 rpfq=1 rp=3c2a dt=23301/73 dn=2 df=1882 of=0 ri=2126 ql=2 b=10

  1 c=4011 g=4012 pq=1 pqc=4011 qp=0 rpfq=3 rp=39a6 dt=78073/1 dn=2 df=1402 of=0 ri=1875 ql=46 b=10

  2 c=4010 g=4010 pq=1 pqc=4010 qp=0 rpfq=-5 rp=1d12 dt=16646/0 dn=2 df=3140 of=0 ri=2080 ql=0 b=10

  3 c=4012 g=4013 pq=1 pqc=4012 qp=1 rpfq=3 rp=2b50 dt=21159/1 dn=2 df=2230 of=0 ri=1923 ql=72 b=10

  4 c=4012 g=4013 pq=1 pqc=4012 qp=1 rpfq=3 rp=1644 dt=5783/1 dn=2 df=3348 of=0 ri=2805 ql=7 b=10

  5 c=4012 g=4013 pq=0 pqc=4011 qp=1 rpfq=3 rp=1aac dt=5879/1 dn=2 df=3140 of=0 ri=2066 ql=10 b=10

  6 c=4012 g=4013 pq=1 pqc=4012 qp=1 rpfq=3 rp=ed8 dt=5847/1 dn=2 df=3797 of=0 ri=1266 ql=10 b=10

  7 c=4012 g=4013 pq=1 pqc=4012 qp=1 rpfq=3 rp=1fa2 dt=6199/1 dn=2 df=2795 of=0 ri=2162 ql=28 b=10

rcu_bh:

  0 c=-268 g=-268 pq=1 pqc=-268 qp=0 rpfq=-145 rp=21d6 dt=23301/73 dn=2 df=0 of=0 ri=0 ql=0 b=10

  1 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-170 rp=20ce dt=78073/1 dn=2 df=26 of=0 ri=5 ql=0 b=10

  2 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-83 rp=fbd dt=16646/0 dn=2 df=28 of=0 ri=4 ql=0 b=10

  3 c=-268 g=-268 pq=1 pqc=-268 qp=0 rpfq=-105 rp=178c dt=21159/1 dn=2 df=28 of=0 ri=2 ql=0 b=10

  4 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-30 rp=b54 dt=5783/1 dn=2 df=32 of=0 ri=0 ql=0 b=10

  5 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-29 rp=df5 dt=5879/1 dn=2 df=30 of=0 ri=3 ql=0 b=10

  6 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-28 rp=788 dt=5847/1 dn=2 df=32 of=0 ri=0 ql=0 b=10

  7 c=-268 g=-268 pq=1 pqc=-268 qp=1 rpfq=-53 rp=1098 dt=6199/1 dn=2 df=30 of=0 ri=3 ql=0 b=10

The first section lists the rcu_data structures for rcu, the second for

rcu_bh.  Each section has one line per CPU, or eight for this 8-CPU system.

The fields are as follows:

o	The number at the beginning of each line is the CPU number.

	CPUs numbers followed by an exclamation mark are offline,

	but have been online at least once since boot.	There will be

	no output for CPUs that have never been online, which can be

	a good thing in the surprisingly common case where NR_CPUS is

	substantially larger than the number of actual CPUs.

o	"c" is the count of grace periods that this CPU believes have

	completed.  CPUs in dynticks idle mode may lag quite a ways

	behind, for example, CPU 4 under "rcu" above, which has slept

	through the past 25 RCU grace periods.	It is not unusual to

	see CPUs lagging by thousands of grace periods.

o	"g" is the count of grace periods that this CPU believes have

	started.  Again, CPUs in dynticks idle mode may lag behind.

	If the "c" and "g" values are equal, this CPU has already

	reported a quiescent state for the last RCU grace period that

	it is aware of, otherwise, the CPU believes that it owes RCU a

	quiescent state.

o	"pq" indicates that this CPU has passed through a quiescent state

	for the current grace period.  It is possible for "pq" to be

	"1" and "c" different than "g", which indicates that although

	the CPU has passed through a quiescent state, either (1) this

	CPU has not yet reported that fact, (2) some other CPU has not

	yet reported for this grace period, or (3) both.

o	"pqc" indicates which grace period the last-observed quiescent

	state for this CPU corresponds to.  This is important for handling

	the race between CPU 0 reporting an extended dynticks-idle

	quiescent state for CPU 1 and CPU 1 suddenly waking up and

	reporting its own quiescent state.  If CPU 1 was the last CPU

	for the current grace period, then the CPU that loses this race

	will attempt to incorrectly mark CPU 1 as having checked in for

	the next grace period!

o	"qp" indicates that RCU still expects a quiescent state from

	this CPU.

o	"rpfq" is the number of rcu_pending() calls on this CPU required

	to induce this CPU to invoke force_quiescent_state().

o	"rp" is low-order four hex digits of the count of how many times

	rcu_pending() has been invoked on this CPU.

o	"dt" is the current value of the dyntick counter that is incremented

	when entering or leaving dynticks idle state, either by the

	scheduler or by irq.  The number after the "/" is the interrupt

	nesting depth when in dyntick-idle state, or one greater than

	the interrupt-nesting depth otherwise.

	This field is displayed only for CONFIG_NO_HZ kernels.

o	"dn" is the current value of the dyntick counter that is incremented

	when entering or leaving dynticks idle state via NMI.  If both

	the "dt" and "dn" values are even, then this CPU is in dynticks

	idle mode and may be ignored by RCU.  If either of these two

	counters is odd, then RCU must be alert to the possibility of

	an RCU read-side critical section running on this CPU.

	This field is displayed only for CONFIG_NO_HZ kernels.

o	"df" is the number of times that some other CPU has forced a

	quiescent state on behalf of this CPU due to this CPU being in

	dynticks-idle state.

	This field is displayed only for CONFIG_NO_HZ kernels.

o	"of" is the number of times that some other CPU has forced a

	quiescent state on behalf of this CPU due to this CPU being

	offline.  In a perfect world, this might neve happen, but it

	turns out that offlining and onlining a CPU can take several grace

	periods, and so there is likely to be an extended period of time

	when RCU believes that the CPU is online when it really is not.

	Please note that erring in the other direction (RCU believing a

	CPU is offline when it is really alive and kicking) is a fatal

	error, so it makes sense to err conservatively.

o	"ri" is the number of times that RCU has seen fit to send a

	reschedule IPI to this CPU in order to get it to report a

	quiescent state.

o	"ql" is the number of RCU callbacks currently residing on

	this CPU.  This is the total number of callbacks, regardless

	of what state they are in (new, waiting for grace period to

	start, waiting for grace period to end, ready to invoke).

o	"b" is the batch limit for this CPU.  If more than this number

	of RCU callbacks is ready to invoke, then the remainder will

	be deferred.

The output of "cat rcu/rcugp" looks as follows:

rcu: completed=33062  gpnum=33063

rcu_bh: completed=464  gpnum=464

Again, this output is for both "rcu" and "rcu_bh".  The fields are

taken from the rcu_state structure, and are as follows:

o	"completed" is the number of grace periods that have completed.

	It is comparable to the "c" field from rcu/rcudata in that a

	CPU whose "c" field matches the value of "completed" is aware

	that the corresponding RCU grace period has completed.

o	"gpnum" is the number of grace periods that have started.  It is

	comparable to the "g" field from rcu/rcudata in that a CPU

	whose "g" field matches the value of "gpnum" is aware that the

	corresponding RCU grace period has started.

	If these two fields are equal (as they are for "rcu_bh" above),

	then there is no grace period in progress, in other words, RCU

	is idle.  On the other hand, if the two fields differ (as they

	do for "rcu" above), then an RCU grace period is in progress.

The output of "cat rcu/rcuhier" looks as follows, with very long lines:

c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6

1/1 0:127 ^0    

3/3 0:35 ^0    0/0 36:71 ^1    0/0 72:107 ^2    0/0 108:127 ^3    

3/3f 0:5 ^0    2/3 6:11 ^1    0/0 12:17 ^2    0/0 18:23 ^3    0/0 24:29 ^4    0/0 30:35 ^5    0/0 36:41 ^0    0/0 42:47 ^1    0/0 48:53 ^2    0/0 54:59 ^3    0/0 60:65 ^4    0/0 66:71 ^5    0/0 72:77 ^0    0/0 78:83 ^1    0/0 84:89 ^2    0/0 90:95 ^3    0/0 96:101 ^4    0/0 102:107 ^5    0/0 108:113 ^0    0/0 114:119 ^1    0/0 120:125 ^2    0/0 126:127 ^3    

rcu_bh:

c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0

0/1 0:127 ^0    

0/3 0:35 ^0    0/0 36:71 ^1    0/0 72:107 ^2    0/0 108:127 ^3    

0/3f 0:5 ^0    0/3 6:11 ^1    0/0 12:17 ^2    0/0 18:23 ^3    0/0 24:29 ^4    0/0 30:35 ^5    0/0 36:41 ^0    0/0 42:47 ^1    0/0 48:53 ^2    0/0 54:59 ^3    0/0 60:65 ^4    0/0 66:71 ^5    0/0 72:77 ^0    0/0 78:83 ^1    0/0 84:89 ^2    0/0 90:95 ^3    0/0 96:101 ^4    0/0 102:107 ^5    0/0 108:113 ^0    0/0 114:119 ^1    0/0 120:125 ^2    0/0 126:127 ^3

This is once again split into "rcu" and "rcu_bh" portions.  The fields are

as follows:

o	"c" is exactly the same as "completed" under rcu/rcugp.

o	"g" is exactly the same as "gpnum" under rcu/rcugp.

o	"s" is the "signaled" state that drives force_quiescent_state()'s

	state machine.

o	"jfq" is the number of jiffies remaining for this grace period

	before force_quiescent_state() is invoked to help push things

	along.  Note that CPUs in dyntick-idle mode thoughout the grace

	period will not report on their own, but rather must be check by

	some other CPU via force_quiescent_state().

o	"j" is the low-order four hex digits of the jiffies counter.

	Yes, Paul did run into a number of problems that turned out to

	be due to the jiffies counter no longer counting.  Why do you ask?

o	"nfqs" is the number of calls to force_quiescent_state() since

	boot.

o	"nfqsng" is the number of useless calls to force_quiescent_state(),

	where there wasn't actually a grace period active.  This can

	happen due to races.  The number in parentheses is the difference

	between "nfqs" and "nfqsng", or the number of times that

	force_quiescent_state() actually did some real work.

o	"fqlh" is the number of calls to force_quiescent_state() that

	exited immediately (without even being counted in nfqs above)

	due to contention on ->fqslock.

o	Each element of the form "1/1 0:127 ^0" represents one struct

	rcu_node.  Each line represents one level of the hierarchy, from

	root to leaves.  It is best to think of the rcu_data structures

	as forming yet another level after the leaves.  Note that there

	might be either one, two, or three levels of rcu_node structures,

	depending on the relationship between CONFIG_RCU_FANOUT and

	CONFIG_NR_CPUS.

	o	The numbers separated by the "/" are the qsmask followed

		by the qsmaskinit.  The qsmask will have one bit

		set for each entity in the next lower level that

		has not yet checked in for the current grace period.

		The qsmaskinit will have one bit for each entity that is

		currently expected to check in during each grace period.

		The value of qsmaskinit is assigned to that of qsmask

		at the beginning of each grace period.

		For example, for "rcu", the qsmask of the first entry

		of the lowest level is 0x14, meaning that we are still

		waiting for CPUs 2 and 4 to check in for the current

		grace period.

	o	The numbers separated by the ":" are the range of CPUs

		served by this struct rcu_node.  This can be helpful

		in working out how the hierarchy is wired together.

		For example, the first entry at the lowest level shows

		"0:5", indicating that it covers CPUs 0 through 5.

	o	The number after the "^" indicates the bit in the

		next higher level rcu_node structure that this

		rcu_node structure corresponds to.

		For example, the first entry at the lowest level shows

		"^0", indicating that it corresponds to bit zero in

		the first entry at the middle level.

queue and specific I/O schedulers.  Unless stated otherwise, elevator is used

to refer to both parts and I/O scheduler to specific I/O schedulers.

Block layer implements generic dispatch queue in ll_rw_blk.c and elevator.c.

Block layer implements generic dispatch queue in block/*.c.

The generic dispatch queue is responsible for properly ordering barrier

requests, requeueing, handling non-fs requests and all other subtleties.

change to another one dynamically.

A block layer call to the i/o scheduler follows the convention elv_xxx(). This

calls elevator_xxx_fn in the elevator switch (drivers/block/elevator.c). Oh,

xxx and xxx might not match exactly, but use your imagination. If an elevator

calls elevator_xxx_fn in the elevator switch (block/elevator.c). Oh, xxx

and xxx might not match exactly, but use your imagination. If an elevator

doesn't implement a function, the switch does nothing or some minimal house

keeping work.