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Diffstat (limited to 'Documentation/RCU/trace.txt')
| -rw-r--r-- | Documentation/RCU/trace.txt | 132 |
1 files changed, 124 insertions, 8 deletions
diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index a851118775d8..ff6d3f10c82f 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -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. |