rcu: document TINY_RCU and TINY_PREEMPT_RCU tracing.
Add the required verbiage to Documentation/RCU/trace.txt. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
Paul E. McKenney
parent
9e571a82f0
commit
8e79e1f961
|
|
@ -1,18 +1,22 @@
|
|||
CONFIG_RCU_TRACE debugfs Files and Formats
|
||||
|
||||
|
||||
The rcutree implementation of RCU provides 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.
|
||||
The following sections describe the debugfs files and formats.
|
||||
The rcutree and rcutiny 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.
|
||||
The following sections describe the debugfs files and formats, first
|
||||
for rcutree and next for rcutiny.
|
||||
|
||||
|
||||
Hierarchical RCU debugfs Files and Formats
|
||||
CONFIG_TREE_RCU and CONFIG_TREE_PREEMPT_RCU debugfs Files and Formats
|
||||
|
||||
This implementation of RCU provides three debugfs files under the
|
||||
These implementations of RCU provides five 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).
|
||||
rcu_data), rcu/rcudata.csv (which is a .csv spreadsheet version of
|
||||
rcu/rcudata), rcu/rcugp (which displays grace-period counters),
|
||||
rcu/rcuhier (which displays the struct rcu_node hierarchy), and
|
||||
rcu/rcu_pending (which displays counts of the reasons that the
|
||||
rcu_pending() function decided that there was core RCU work to do).
|
||||
|
||||
The output of "cat rcu/rcudata" looks as follows:
|
||||
|
||||
|
|
@ -326,3 +330,115 @@ o "nn" is the number of times that this CPU needed nothing. Alert
|
|||
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
|
||||
is due to short-circuit evaluation in rcu_pending().
|
||||
|
||||
|
||||
CONFIG_TINY_RCU and CONFIG_TINY_PREEMPT_RCU debugfs Files and Formats
|
||||
|
||||
These implementations of RCU provides a single debugfs file under the
|
||||
top-level directory RCU, namely rcu/rcudata, which displays fields in
|
||||
rcu_bh_ctrlblk, rcu_sched_ctrlblk and, for CONFIG_TINY_PREEMPT_RCU,
|
||||
rcu_preempt_ctrlblk.
|
||||
|
||||
The output of "cat rcu/rcudata" is as follows:
|
||||
|
||||
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.
|
||||
|
|
|
|||
Loading…
Reference in New Issue