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authorLinus Torvalds <torvalds@linux-foundation.org>2008-12-30 16:10:19 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-30 16:10:19 -0800
commit5f34fe1cfc1bdd8b4711bbe37421fba4ed0d1ed4 (patch)
tree85b21c8bb0e53005bd970d648ca093acfd0584a3 /Documentation/RCU
parenteca1bf5b4fab56d2feb1572d34d59fcd92ea7df3 (diff)
parent6638101c1124c19c8a65b1645e4ecd09e0572f3e (diff)
downloadlinux-linaro-stable-5f34fe1cfc1bdd8b4711bbe37421fba4ed0d1ed4.tar.gz
Merge branch 'core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (63 commits) stacktrace: provide save_stack_trace_tsk() weak alias rcu: provide RCU options on non-preempt architectures too printk: fix discarding message when recursion_bug futex: clean up futex_(un)lock_pi fault handling "Tree RCU": scalable classic RCU implementation futex: rename field in futex_q to clarify single waiter semantics x86/swiotlb: add default swiotlb_arch_range_needs_mapping x86/swiotlb: add default phys<->bus conversion x86: unify pci iommu setup and allow swiotlb to compile for 32 bit x86: add swiotlb allocation functions swiotlb: consolidate swiotlb info message printing swiotlb: support bouncing of HighMem pages swiotlb: factor out copy to/from device swiotlb: add arch hook to force mapping swiotlb: allow architectures to override phys<->bus<->phys conversions swiotlb: add comment where we handle the overflow of a dma mask on 32 bit rcu: fix rcutorture behavior during reboot resources: skip sanity check of busy resources swiotlb: move some definitions to header swiotlb: allow architectures to override swiotlb pool allocation ... Fix up trivial conflicts in arch/x86/kernel/Makefile arch/x86/mm/init_32.c include/linux/hardirq.h as per Ingo's suggestions.
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/00-INDEX2
-rw-r--r--Documentation/RCU/trace.txt413
2 files changed, 415 insertions, 0 deletions
diff --git a/Documentation/RCU/00-INDEX b/Documentation/RCU/00-INDEX
index 461481dfb7c3..7dc0695a8f90 100644
--- a/Documentation/RCU/00-INDEX
+++ b/Documentation/RCU/00-INDEX
@@ -16,6 +16,8 @@ RTFP.txt
- 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
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
new file mode 100644
index 000000000000..068848240a8b
--- /dev/null
+++ b/Documentation/RCU/trace.txt
@@ -0,0 +1,413 @@
+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.