f347c9d269
Once upon a time, we only support accounting thrashing of page cache.
Then Joonsoo introduced workingset detection for anonymous pages and we
gained the ability to account thrashing of them[1].
So let delayacct account both the thrashing of page cache and anonymous
pages, this could make the codes more consistent and simpler.
[1] commit aae466b005 ("mm/swap: implement workingset detection for anonymous LRU")
Link: https://lkml.kernel.org/r/20220805033838.1714674-1-yang.yang29@zte.com.cn
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
131 lines
4.6 KiB
ReStructuredText
131 lines
4.6 KiB
ReStructuredText
================
|
|
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
|
|
e) thrashing
|
|
f) direct compact
|
|
g) write-protect copy
|
|
|
|
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/uapi/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, thrash page
|
|
cache, direct compact, write-protect copy 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 disabled by default at boot up.
|
|
To enable, add::
|
|
|
|
delayacct
|
|
|
|
to the kernel boot options. The rest of the instructions below assume this has
|
|
been done. Alternatively, use sysctl kernel.task_delayacct to switch the state
|
|
at runtime. Note however that only tasks started after enabling it will have
|
|
delayacct information.
|
|
|
|
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 [-dilv] [-t tgid] [-p pid]
|
|
|
|
Get delays, since system boot, for pid 10::
|
|
|
|
# ./getdelays -d -p 10
|
|
(output similar to next case)
|
|
|
|
Get sum of delays, since system boot, for all pids with tgid 5::
|
|
|
|
# ./getdelays -d -t 5
|
|
print delayacct stats ON
|
|
TGID 5
|
|
|
|
|
|
CPU count real total virtual total delay total delay average
|
|
8 7000000 6872122 3382277 0.423ms
|
|
IO count delay total delay average
|
|
0 0 0ms
|
|
SWAP count delay total delay average
|
|
0 0 0ms
|
|
RECLAIM count delay total delay average
|
|
0 0 0ms
|
|
THRASHING count delay total delay average
|
|
0 0 0ms
|
|
COMPACT count delay total delay average
|
|
0 0 0ms
|
|
WPCOPY count delay total delay average
|
|
0 0 0ms
|
|
|
|
Get IO accounting for pid 1, it works only with -p::
|
|
|
|
# ./getdelays -i -p 1
|
|
printing IO accounting
|
|
linuxrc: read=65536, write=0, cancelled_write=0
|
|
|
|
The above command can be used with -v to get more debug information.
|