e59fb3120b
Commit d09b62d fixed grace-period synchronization, but left some smp_mb()
invocations in rcu_process_callbacks() that are no longer needed, but
sheer paranoia prevented them from being removed. This commit removes
them and provides a proof of correctness in their absence. It also adds
a memory barrier to rcu_report_qs_rsp() immediately before the update to
rsp->completed in order to handle the theoretical possibility that the
compiler or CPU might move massive quantities of code into a lock-based
critical section. This also proves that the sheer paranoia was not
entirely unjustified, at least from a theoretical point of view.
In addition, the old dyntick-idle synchronization depended on the fact
that grace periods were many milliseconds in duration, so that it could
be assumed that no dyntick-idle CPU could reorder a memory reference
across an entire grace period. Unfortunately for this design, the
addition of expedited grace periods breaks this assumption, which has
the unfortunate side-effect of requiring atomic operations in the
functions that track dyntick-idle state for RCU. (There is some hope
that the algorithms used in user-level RCU might be applied here, but
some work is required to handle the NMIs that user-space applications
can happily ignore. For the short term, better safe than sorry.)
This proof assumes that neither compiler nor CPU will allow a lock
acquisition and release to be reordered, as doing so can result in
deadlock. The proof is as follows:
1. A given CPU declares a quiescent state under the protection of
its leaf rcu_node's lock.
2. If there is more than one level of rcu_node hierarchy, the
last CPU to declare a quiescent state will also acquire the
->lock of the next rcu_node up in the hierarchy, but only
after releasing the lower level's lock. The acquisition of this
lock clearly cannot occur prior to the acquisition of the leaf
node's lock.
3. Step 2 repeats until we reach the root rcu_node structure.
Please note again that only one lock is held at a time through
this process. The acquisition of the root rcu_node's ->lock
must occur after the release of that of the leaf rcu_node.
4. At this point, we set the ->completed field in the rcu_state
structure in rcu_report_qs_rsp(). However, if the rcu_node
hierarchy contains only one rcu_node, then in theory the code
preceding the quiescent state could leak into the critical
section. We therefore precede the update of ->completed with a
memory barrier. All CPUs will therefore agree that any updates
preceding any report of a quiescent state will have happened
before the update of ->completed.
5. Regardless of whether a new grace period is needed, rcu_start_gp()
will propagate the new value of ->completed to all of the leaf
rcu_node structures, under the protection of each rcu_node's ->lock.
If a new grace period is needed immediately, this propagation
will occur in the same critical section that ->completed was
set in, but courtesy of the memory barrier in #4 above, is still
seen to follow any pre-quiescent-state activity.
6. When a given CPU invokes __rcu_process_gp_end(), it becomes
aware of the end of the old grace period and therefore makes
any RCU callbacks that were waiting on that grace period eligible
for invocation.
If this CPU is the same one that detected the end of the grace
period, and if there is but a single rcu_node in the hierarchy,
we will still be in the single critical section. In this case,
the memory barrier in step #4 guarantees that all callbacks will
be seen to execute after each CPU's quiescent state.
On the other hand, if this is a different CPU, it will acquire
the leaf rcu_node's ->lock, and will again be serialized after
each CPU's quiescent state for the old grace period.
On the strength of this proof, this commit therefore removes the memory
barriers from rcu_process_callbacks() and adds one to rcu_report_qs_rsp().
The effect is to reduce the number of memory barriers by one and to
reduce the frequency of execution from about once per scheduling tick
per CPU to once per grace period.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
433 lines
20 KiB
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433 lines
20 KiB
Plaintext
CONFIG_RCU_TRACE debugfs Files and Formats
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The rcutree and rcutiny implementations of RCU provide debugfs trace
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output that summarizes counters and state. This information is useful for
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debugging RCU itself, and can sometimes also help to debug abuses of RCU.
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The following sections describe the debugfs files and formats, first
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for rcutree and next for rcutiny.
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CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
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These implementations of RCU provides five debugfs files under the
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top-level directory RCU: rcu/rcudata (which displays fields in struct
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rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of
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rcu/rcudata), rcu/rcugp (which displays grace-period counters),
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rcu/rcuhier (which displays the struct rcu_node hierarchy), and
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rcu/rcu_pending (which displays counts of the reasons that the
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rcu_pending() function decided that there was core RCU work to do).
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The output of "cat rcu/rcudata" looks as follows:
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rcu_sched:
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0 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=10951/1/0 df=1101 of=0 ri=36 ql=0 b=10
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1 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=16117/1/0 df=1015 of=0 ri=0 ql=0 b=10
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2 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1445/1/0 df=1839 of=0 ri=0 ql=0 b=10
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3 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=6681/1/0 df=1545 of=0 ri=0 ql=0 b=10
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4 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=1003/1/0 df=1992 of=0 ri=0 ql=0 b=10
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5 c=17829 g=17830 pq=1 pqc=17829 qp=1 dt=3887/1/0 df=3331 of=0 ri=4 ql=2 b=10
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6 c=17829 g=17829 pq=1 pqc=17829 qp=0 dt=859/1/0 df=3224 of=0 ri=0 ql=0 b=10
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7 c=17829 g=17830 pq=0 pqc=17829 qp=1 dt=3761/1/0 df=1818 of=0 ri=0 ql=2 b=10
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rcu_bh:
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0 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=10951/1/0 df=0 of=0 ri=0 ql=0 b=10
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1 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=16117/1/0 df=13 of=0 ri=0 ql=0 b=10
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2 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1445/1/0 df=15 of=0 ri=0 ql=0 b=10
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3 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=6681/1/0 df=9 of=0 ri=0 ql=0 b=10
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4 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=1003/1/0 df=15 of=0 ri=0 ql=0 b=10
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5 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3887/1/0 df=15 of=0 ri=0 ql=0 b=10
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6 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=859/1/0 df=15 of=0 ri=0 ql=0 b=10
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7 c=-275 g=-275 pq=1 pqc=-275 qp=0 dt=3761/1/0 df=15 of=0 ri=0 ql=0 b=10
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The first section lists the rcu_data structures for rcu_sched, the second
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for rcu_bh. Note that CONFIG_TREE_PREEMPT_RCU kernels will have an
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additional section for rcu_preempt. Each section has one line per CPU,
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or eight for this 8-CPU system. The fields are as follows:
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o The number at the beginning of each line is the CPU number.
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CPUs numbers followed by an exclamation mark are offline,
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but have been online at least once since boot. There will be
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no output for CPUs that have never been online, which can be
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a good thing in the surprisingly common case where NR_CPUS is
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substantially larger than the number of actual CPUs.
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o "c" is the count of grace periods that this CPU believes have
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completed. CPUs in dynticks idle mode may lag quite a ways
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behind, for example, CPU 4 under "rcu_sched" above, which has
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slept through the past 25 RCU grace periods. It is not unusual
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to see CPUs lagging by thousands of grace periods.
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o "g" is the count of grace periods that this CPU believes have
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started. Again, CPUs in dynticks idle mode may lag behind.
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If the "c" and "g" values are equal, this CPU has already
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reported a quiescent state for the last RCU grace period that
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it is aware of, otherwise, the CPU believes that it owes RCU a
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quiescent state.
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o "pq" indicates that this CPU has passed through a quiescent state
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for the current grace period. It is possible for "pq" to be
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"1" and "c" different than "g", which indicates that although
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the CPU has passed through a quiescent state, either (1) this
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CPU has not yet reported that fact, (2) some other CPU has not
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yet reported for this grace period, or (3) both.
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o "pqc" indicates which grace period the last-observed quiescent
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state for this CPU corresponds to. This is important for handling
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the race between CPU 0 reporting an extended dynticks-idle
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quiescent state for CPU 1 and CPU 1 suddenly waking up and
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reporting its own quiescent state. If CPU 1 was the last CPU
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for the current grace period, then the CPU that loses this race
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will attempt to incorrectly mark CPU 1 as having checked in for
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the next grace period!
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o "qp" indicates that RCU still expects a quiescent state from
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this CPU.
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o "dt" is the current value of the dyntick counter that is incremented
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when entering or leaving dynticks idle state, either by the
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scheduler or by irq. The number after the first "/" is the
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interrupt nesting depth when in dyntick-idle state, or one
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greater than the interrupt-nesting depth otherwise. The number
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after the second "/" is the NMI nesting depth.
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This field is displayed only for CONFIG_NO_HZ kernels.
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o "df" is the number of times that some other CPU has forced a
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quiescent state on behalf of this CPU due to this CPU being in
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dynticks-idle state.
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This field is displayed only for CONFIG_NO_HZ kernels.
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o "of" is the number of times that some other CPU has forced a
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quiescent state on behalf of this CPU due to this CPU being
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offline. In a perfect world, this might neve happen, but it
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turns out that offlining and onlining a CPU can take several grace
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periods, and so there is likely to be an extended period of time
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when RCU believes that the CPU is online when it really is not.
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Please note that erring in the other direction (RCU believing a
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CPU is offline when it is really alive and kicking) is a fatal
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error, so it makes sense to err conservatively.
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o "ri" is the number of times that RCU has seen fit to send a
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reschedule IPI to this CPU in order to get it to report a
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quiescent state.
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o "ql" is the number of RCU callbacks currently residing on
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this CPU. This is the total number of callbacks, regardless
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of what state they are in (new, waiting for grace period to
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start, waiting for grace period to end, ready to invoke).
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o "b" is the batch limit for this CPU. If more than this number
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of RCU callbacks is ready to invoke, then the remainder will
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be deferred.
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o "ci" is the number of RCU callbacks that have been invoked for
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this CPU. Note that ci+ql is the number of callbacks that have
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been registered in absence of CPU-hotplug activity.
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o "co" is the number of RCU callbacks that have been orphaned due to
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this CPU going offline. These orphaned callbacks have been moved
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to an arbitrarily chosen online CPU.
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o "ca" is the number of RCU callbacks that have been adopted due to
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other CPUs going offline. Note that ci+co-ca+ql is the number of
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RCU callbacks registered on this CPU.
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There is also an rcu/rcudata.csv file with the same information in
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comma-separated-variable spreadsheet format.
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The output of "cat rcu/rcugp" looks as follows:
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rcu_sched: completed=33062 gpnum=33063
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rcu_bh: completed=464 gpnum=464
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Again, this output is for both "rcu_sched" and "rcu_bh". Note that
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kernels built with CONFIG_TREE_PREEMPT_RCU will have an additional
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"rcu_preempt" line. The fields are taken from the rcu_state structure,
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and are as follows:
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o "completed" is the number of grace periods that have completed.
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It is comparable to the "c" field from rcu/rcudata in that a
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CPU whose "c" field matches the value of "completed" is aware
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that the corresponding RCU grace period has completed.
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o "gpnum" is the number of grace periods that have started. It is
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comparable to the "g" field from rcu/rcudata in that a CPU
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whose "g" field matches the value of "gpnum" is aware that the
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corresponding RCU grace period has started.
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If these two fields are equal (as they are for "rcu_bh" above),
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then there is no grace period in progress, in other words, RCU
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is idle. On the other hand, if the two fields differ (as they
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do for "rcu_sched" above), then an RCU grace period is in progress.
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The output of "cat rcu/rcuhier" looks as follows, with very long lines:
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c=6902 g=6903 s=2 jfq=3 j=72c7 nfqs=13142/nfqsng=0(13142) fqlh=6
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1/1 .>. 0:127 ^0
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3/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
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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
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rcu_bh:
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c=-226 g=-226 s=1 jfq=-5701 j=72c7 nfqs=88/nfqsng=0(88) fqlh=0
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0/1 .>. 0:127 ^0
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0/3 .>. 0:35 ^0 0/0 .>. 36:71 ^1 0/0 .>. 72:107 ^2 0/0 .>. 108:127 ^3
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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
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This is once again split into "rcu_sched" and "rcu_bh" portions,
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and CONFIG_TREE_PREEMPT_RCU kernels will again have an additional
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"rcu_preempt" section. The fields are as follows:
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o "c" is exactly the same as "completed" under rcu/rcugp.
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o "g" is exactly the same as "gpnum" under rcu/rcugp.
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o "s" is the "signaled" state that drives force_quiescent_state()'s
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state machine.
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o "jfq" is the number of jiffies remaining for this grace period
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before force_quiescent_state() is invoked to help push things
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along. Note that CPUs in dyntick-idle mode throughout the grace
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period will not report on their own, but rather must be check by
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some other CPU via force_quiescent_state().
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o "j" is the low-order four hex digits of the jiffies counter.
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Yes, Paul did run into a number of problems that turned out to
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be due to the jiffies counter no longer counting. Why do you ask?
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o "nfqs" is the number of calls to force_quiescent_state() since
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boot.
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o "nfqsng" is the number of useless calls to force_quiescent_state(),
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where there wasn't actually a grace period active. This can
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happen due to races. The number in parentheses is the difference
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between "nfqs" and "nfqsng", or the number of times that
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force_quiescent_state() actually did some real work.
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o "fqlh" is the number of calls to force_quiescent_state() that
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exited immediately (without even being counted in nfqs above)
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due to contention on ->fqslock.
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o Each element of the form "1/1 0:127 ^0" represents one struct
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rcu_node. Each line represents one level of the hierarchy, from
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root to leaves. It is best to think of the rcu_data structures
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as forming yet another level after the leaves. Note that there
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might be either one, two, or three levels of rcu_node structures,
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depending on the relationship between CONFIG_RCU_FANOUT and
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CONFIG_NR_CPUS.
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o The numbers separated by the "/" are the qsmask followed
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by the qsmaskinit. The qsmask will have one bit
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set for each entity in the next lower level that
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has not yet checked in for the current grace period.
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The qsmaskinit will have one bit for each entity that is
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currently expected to check in during each grace period.
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The value of qsmaskinit is assigned to that of qsmask
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at the beginning of each grace period.
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For example, for "rcu_sched", the qsmask of the first
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entry of the lowest level is 0x14, meaning that we
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are still waiting for CPUs 2 and 4 to check in for the
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current grace period.
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o The characters separated by the ">" indicate the state
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of the blocked-tasks lists. A "T" preceding the ">"
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indicates that at least one task blocked in an RCU
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read-side critical section blocks the current grace
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period, while a "." preceding the ">" indicates otherwise.
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The character following the ">" indicates similarly for
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the next grace period. A "T" should appear in this
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field only for rcu-preempt.
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o The numbers separated by the ":" are the range of CPUs
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served by this struct rcu_node. This can be helpful
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in working out how the hierarchy is wired together.
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For example, the first entry at the lowest level shows
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"0:5", indicating that it covers CPUs 0 through 5.
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o The number after the "^" indicates the bit in the
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next higher level rcu_node structure that this
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rcu_node structure corresponds to.
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For example, the first entry at the lowest level shows
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"^0", indicating that it corresponds to bit zero in
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the first entry at the middle level.
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The output of "cat rcu/rcu_pending" looks as follows:
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rcu_sched:
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0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741
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1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792
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2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629
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3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nf=207 nn=137723
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4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nf=3529 nn=123110
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5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nf=201 nn=137456
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6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nf=4202 nn=120834
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7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nf=41 nn=144888
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rcu_bh:
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0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nf=2 nn=145314
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1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nf=3 nn=143180
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2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nf=0 nn=117936
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3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nf=0 nn=134863
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4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nf=0 nn=110671
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5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nf=0 nn=133235
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6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nf=2 nn=110921
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7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nf=0 nn=118542
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As always, this is once again split into "rcu_sched" and "rcu_bh"
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portions, with CONFIG_TREE_PREEMPT_RCU kernels having an additional
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"rcu_preempt" section. The fields are as follows:
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o "np" is the number of times that __rcu_pending() has been invoked
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for the corresponding flavor of RCU.
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o "qsp" is the number of times that the RCU was waiting for a
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quiescent state from this CPU.
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o "rpq" is the number of times that the CPU had passed through
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a quiescent state, but not yet reported it to RCU.
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o "cbr" is the number of times that this CPU had RCU callbacks
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that had passed through a grace period, and were thus ready
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to be invoked.
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o "cng" is the number of times that this CPU needed another
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grace period while RCU was idle.
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o "gpc" is the number of times that an old grace period had
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completed, but this CPU was not yet aware of it.
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o "gps" is the number of times that a new grace period had started,
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but this CPU was not yet aware of it.
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|
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o "nf" is the number of times that this CPU suspected that the
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current grace period had run for too long, and thus needed to
|
|
be forced.
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|
|
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Please note that "forcing" consists of sending resched IPIs
|
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to holdout CPUs. If that CPU really still is in an old RCU
|
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read-side critical section, then we really do have to wait for it.
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The assumption behing "forcing" is that the CPU is not still in
|
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an old RCU read-side critical section, but has not yet responded
|
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for some other reason.
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|
|
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o "nn" is the number of times that this CPU needed nothing. Alert
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readers will note that the rcu "nn" number for a given CPU very
|
|
closely matches the rcu_bh "np" number for that same CPU. This
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is due to short-circuit evaluation in rcu_pending().
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CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats
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|
|
|
These implementations of RCU provides a single debugfs file under the
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top-level directory RCU, namely rcu/rcudata, which displays fields in
|
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rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
|
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rcu_preempt_ctrlblk.
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|
|
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The output of "cat rcu/rcudata" is as follows:
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|
|
|
rcu_preempt: qlen=24 gp=1097669 g197/p197/c197 tasks=...
|
|
ttb=. btg=no ntb=184 neb=0 nnb=183 j=01f7 bt=0274
|
|
normal balk: nt=1097669 gt=0 bt=371 b=0 ny=25073378 nos=0
|
|
exp balk: bt=0 nos=0
|
|
rcu_sched: qlen: 0
|
|
rcu_bh: qlen: 0
|
|
|
|
This is split into rcu_preempt, rcu_sched, and rcu_bh sections, with the
|
|
rcu_preempt section appearing only in CONFIG_TINY_PREEMPT_RCU builds.
|
|
The last three lines of the rcu_preempt section appear only in
|
|
CONFIG_RCU_BOOST kernel builds. The fields are as follows:
|
|
|
|
o "qlen" is the number of RCU callbacks currently waiting either
|
|
for an RCU grace period or waiting to be invoked. This is the
|
|
only field present for rcu_sched and rcu_bh, due to the
|
|
short-circuiting of grace period in those two cases.
|
|
|
|
o "gp" is the number of grace periods that have completed.
|
|
|
|
o "g197/p197/c197" displays the grace-period state, with the
|
|
"g" number being the number of grace periods that have started
|
|
(mod 256), the "p" number being the number of grace periods
|
|
that the CPU has responded to (also mod 256), and the "c"
|
|
number being the number of grace periods that have completed
|
|
(once again mode 256).
|
|
|
|
Why have both "gp" and "g"? Because the data flowing into
|
|
"gp" is only present in a CONFIG_RCU_TRACE kernel.
|
|
|
|
o "tasks" is a set of bits. The first bit is "T" if there are
|
|
currently tasks that have recently blocked within an RCU
|
|
read-side critical section, the second bit is "N" if any of the
|
|
aforementioned tasks are blocking the current RCU grace period,
|
|
and the third bit is "E" if any of the aforementioned tasks are
|
|
blocking the current expedited grace period. Each bit is "."
|
|
if the corresponding condition does not hold.
|
|
|
|
o "ttb" is a single bit. It is "B" if any of the blocked tasks
|
|
need to be priority boosted and "." otherwise.
|
|
|
|
o "btg" indicates whether boosting has been carried out during
|
|
the current grace period, with "exp" indicating that boosting
|
|
is in progress for an expedited grace period, "no" indicating
|
|
that boosting has not yet started for a normal grace period,
|
|
"begun" indicating that boosting has bebug for a normal grace
|
|
period, and "done" indicating that boosting has completed for
|
|
a normal grace period.
|
|
|
|
o "ntb" is the total number of tasks subjected to RCU priority boosting
|
|
periods since boot.
|
|
|
|
o "neb" is the number of expedited grace periods that have had
|
|
to resort to RCU priority boosting since boot.
|
|
|
|
o "nnb" is the number of normal grace periods that have had
|
|
to resort to RCU priority boosting since boot.
|
|
|
|
o "j" is the low-order 12 bits of the jiffies counter in hexadecimal.
|
|
|
|
o "bt" is the low-order 12 bits of the value that the jiffies counter
|
|
will have at the next time that boosting is scheduled to begin.
|
|
|
|
o In the line beginning with "normal balk", the fields are as follows:
|
|
|
|
o "nt" is the number of times that the system balked from
|
|
boosting because there were no blocked tasks to boost.
|
|
Note that the system will balk from boosting even if the
|
|
grace period is overdue when the currently running task
|
|
is looping within an RCU read-side critical section.
|
|
There is no point in boosting in this case, because
|
|
boosting a running task won't make it run any faster.
|
|
|
|
o "gt" is the number of times that the system balked
|
|
from boosting because, although there were blocked tasks,
|
|
none of them were preventing the current grace period
|
|
from completing.
|
|
|
|
o "bt" is the number of times that the system balked
|
|
from boosting because boosting was already in progress.
|
|
|
|
o "b" is the number of times that the system balked from
|
|
boosting because boosting had already completed for
|
|
the grace period in question.
|
|
|
|
o "ny" is the number of times that the system balked from
|
|
boosting because it was not yet time to start boosting
|
|
the grace period in question.
|
|
|
|
o "nos" is the number of times that the system balked from
|
|
boosting for inexplicable ("not otherwise specified")
|
|
reasons. This can actually happen due to races involving
|
|
increments of the jiffies counter.
|
|
|
|
o In the line beginning with "exp balk", the fields are as follows:
|
|
|
|
o "bt" is the number of times that the system balked from
|
|
boosting because there were no blocked tasks to boost.
|
|
|
|
o "nos" is the number of times that the system balked from
|
|
boosting for inexplicable ("not otherwise specified")
|
|
reasons.
|