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Diffstat (limited to 'Documentation/accounting/delay-accounting.txt')
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diff --git a/Documentation/accounting/delay-accounting.txt b/Documentation/accounting/delay-accounting.txt deleted file mode 100644 index 042ea59b5853..000000000000 --- a/Documentation/accounting/delay-accounting.txt +++ /dev/null @@ -1,117 +0,0 @@ -Delay accounting ----------------- - -Tasks encounter delays in execution when they wait -for some kernel resource to become available e.g. a -runnable task may wait for a free CPU to run on. - -The per-task delay accounting functionality measures -the delays experienced by a task while - -a) waiting for a CPU (while being runnable) -b) completion of synchronous block I/O initiated by the task -c) swapping in pages -d) memory reclaim - -and makes these statistics available to userspace through -the taskstats interface. - -Such delays provide feedback for setting a task's cpu priority, -io priority and rss limit values appropriately. Long delays for -important tasks could be a trigger for raising its corresponding priority. - -The functionality, through its use of the taskstats interface, also provides -delay statistics aggregated for all tasks (or threads) belonging to a -thread group (corresponding to a traditional Unix process). This is a commonly -needed aggregation that is more efficiently done by the kernel. - -Userspace utilities, particularly resource management applications, can also -aggregate delay statistics into arbitrary groups. To enable this, delay -statistics of a task are available both during its lifetime as well as on its -exit, ensuring continuous and complete monitoring can be done. - - -Interface ---------- - -Delay accounting uses the taskstats interface which is described -in detail in a separate document in this directory. Taskstats returns a -generic data structure to userspace corresponding to per-pid and per-tgid -statistics. The delay accounting functionality populates specific fields of -this structure. See - include/linux/taskstats.h -for a description of the fields pertaining to delay accounting. -It will generally be in the form of counters returning the cumulative -delay seen for cpu, sync block I/O, swapin, memory reclaim etc. - -Taking the difference of two successive readings of a given -counter (say cpu_delay_total) for a task will give the delay -experienced by the task waiting for the corresponding resource -in that interval. - -When a task exits, records containing the per-task statistics -are sent to userspace without requiring a command. If it is the last exiting -task of a thread group, the per-tgid statistics are also sent. More details -are given in the taskstats interface description. - -The getdelays.c userspace utility in tools/accounting directory allows simple -commands to be run and the corresponding delay statistics to be displayed. It -also serves as an example of using the taskstats interface. - -Usage ------ - -Compile the kernel with - CONFIG_TASK_DELAY_ACCT=y - CONFIG_TASKSTATS=y - -Delay accounting is enabled by default at boot up. -To disable, add - nodelayacct -to the kernel boot options. The rest of the instructions -below assume this has not been done. - -After the system has booted up, use a utility -similar to getdelays.c to access the delays -seen by a given task or a task group (tgid). -The utility also allows a given command to be -executed and the corresponding delays to be -seen. - -General format of the getdelays command - -getdelays [-t tgid] [-p pid] [-c cmd...] - - -Get delays, since system boot, for pid 10 -# ./getdelays -p 10 -(output similar to next case) - -Get sum of delays, since system boot, for all pids with tgid 5 -# ./getdelays -t 5 - - -CPU count real total virtual total delay total - 7876 92005750 100000000 24001500 -IO count delay total - 0 0 -SWAP count delay total - 0 0 -RECLAIM count delay total - 0 0 - -Get delays seen in executing a given simple command -# ./getdelays -c ls / - -bin data1 data3 data5 dev home media opt root srv sys usr -boot data2 data4 data6 etc lib mnt proc sbin subdomain tmp var - - -CPU count real total virtual total delay total - 6 4000250 4000000 0 -IO count delay total - 0 0 -SWAP count delay total - 0 0 -RECLAIM count delay total - 0 0 |