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offcputime_example.txt
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offcputime_example.txt
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Demonstrations of offcputime, the Linux eBPF/bcc version.
This program shows stack traces that were blocked, and the total duration they
were blocked. It works by tracing when threads block and when they return to
CPU, measuring both the time they were blocked (aka the "off-CPU time") and the
blocked kernel stack trace and the task name. This data is summarized in kernel
by summing the blocked time by unique stack trace and task name.
Here is some example output. To explain what we are seeing: the very first
stack trace looks like a page fault (do_page_fault() etc) from the "chmod"
command, and in total was off-CPU for 13 microseconds.
# ./offcputime
Tracing off-CPU time (us) by kernel stack... Hit Ctrl-C to end.
^C
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
wait_on_page_bit_killable
__lock_page_or_retry
filemap_fault
__do_fault
handle_mm_fault
__do_page_fault
do_page_fault
page_fault
chmod
13
schedule
rcu_nocb_kthread
kthread
ret_from_fork
ddebug_tables
rcuos/0
22
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit_lock
__lock_page
lock_page
__do_fault
handle_mm_fault
__do_page_fault
do_page_fault
page_fault
run
27
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
wait_on_page_bit_killable
__lock_page_or_retry
filemap_fault
__do_fault
handle_mm_fault
__do_page_fault
do_page_fault
page_fault
clear_user
padzero
load_elf_binary
search_binary_handler
load_script
search_binary_handler
do_execveat_common.isra.27
run
28
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
wait_on_page_bit_killable
__lock_page_or_retry
filemap_fault
__do_fault
handle_mm_fault
__do_page_fault
do_page_fault
page_fault
run
82
schedule
pipe_wait
pipe_read
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
bash
94
schedule
rcu_gp_kthread
kthread
ret_from_fork
ddebug_tables
rcu_sched
104
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
out_of_line_wait_on_bit
__wait_on_buffer
jbd2_journal_commit_transaction
kjournald2
kthread
ret_from_fork
mb_cache_list
jbd2/xvda1-8
986
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
out_of_line_wait_on_bit
__wait_on_buffer
jbd2_journal_commit_transaction
kjournald2
kthread
ret_from_fork
mb_cache_list
jbd2/xvda1-8
6630
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
out_of_line_wait_on_bit
do_get_write_access
jbd2_journal_get_write_access
__ext4_journal_get_write_access
ext4_mb_mark_diskspace_used
ext4_mb_new_blocks
ext4_ext_map_blocks
ext4_map_blocks
ext4_writepages
do_writepages
__filemap_fdatawrite_range
filemap_flush
ext4_alloc_da_blocks
ext4_rename
ext4_rename2
supervise
6645
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
out_of_line_wait_on_bit
do_get_write_access
jbd2_journal_get_write_access
__ext4_journal_get_write_access
__ext4_new_inode
ext4_create
vfs_create
path_openat
do_filp_open
do_sys_open
sys_open
entry_SYSCALL_64_fastpath
supervise
12702
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/2
16036
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/4
24085
schedule
do_wait
sys_wait4
entry_SYSCALL_64_fastpath
run
233055
schedule
schedule_timeout
io_schedule_timeout
bit_wait_io
__wait_on_bit
wait_on_page_bit
truncate_inode_pages_range
truncate_inode_pages_final
ext4_evict_inode
evict
iput
__dentry_kill
dput
sys_rename
entry_SYSCALL_64_fastpath
supervise
297113
schedule
schedule_timeout
wait_woken
n_tty_read
tty_read
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
bash
1789866
schedule
schedule_timeout
io_schedule_timeout
do_blockdev_direct_IO
__blockdev_direct_IO
blkdev_direct_IO
generic_file_read_iter
blkdev_read_iter
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
dd
3310763
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/1
3999989
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/5
3999995
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/4
3999996
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/0
3999996
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/3
3999998
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/7
3999999
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/2
4000001
schedule
smpboot_thread_fn
kthread
ret_from_fork
watchdog/6
4000001
schedule
do_wait
sys_wait4
entry_SYSCALL_64_fastpath
bash
4039675
schedule
do_nanosleep
hrtimer_nanosleep
sys_nanosleep
entry_SYSCALL_64_fastpath
svscan
5000112
schedule
schedule_hrtimeout_range_clock
schedule_hrtimeout_range
poll_schedule_timeout
do_select
core_sys_select
sys_select
entry_SYSCALL_64_fastpath
snmpd
5998761
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/3
6149779
schedule
schedule_hrtimeout_range_clock
schedule_hrtimeout_range
poll_schedule_timeout
do_select
core_sys_select
sys_select
entry_SYSCALL_64_fastpath
ntpd
6999832
schedule
worker_thread
kthread
ret_from_fork
kworker/u16:2
7131941
schedule
worker_thread
kthread
ret_from_fork
kworker/3:0
7999844
schedule
worker_thread
kthread
ret_from_fork
kworker/1:1
7999872
schedule
worker_thread
kthread
ret_from_fork
kworker/2:1
7999889
schedule
worker_thread
kthread
ret_from_fork
kworker/5:1
7999936
schedule
worker_thread
kthread
ret_from_fork
kworker/7:1
7999938
schedule
worker_thread
kthread
ret_from_fork
kworker/6:1
7999940
schedule
do_nanosleep
hrtimer_nanosleep
sys_nanosleep
entry_SYSCALL_64_fastpath
tail
8000905
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/7
8197046
schedule
pipe_wait
pipe_read
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
readproctitle
8197835
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/4
8201851
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/2
8203375
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/6
8208664
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/5
8209819
schedule
smpboot_thread_fn
kthread
ret_from_fork
ddebug_tables
migration/0
8211292
schedule
smpboot_thread_fn
kthread
ret_from_fork
migration/1
8212100
schedule
worker_thread
kthread
ret_from_fork
kworker/0:2
8270305
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/3
8349697
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/2
8363357
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/1
8365338
schedule
schedule_timeout
xfs_buf_terminate
kthread
ret_from_fork
xfsaild/md0
8371514
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/4
8384013
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/5
8390016
schedule
rcu_nocb_kthread
kthread
ret_from_fork
ddebug_tables
rcuos/0
8405428
schedule
schedule_timeout
rcu_gp_kthread
kthread
ret_from_fork
ddebug_tables
rcu_sched
8406930
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/7
8409575
schedule
rcu_nocb_kthread
kthread
ret_from_fork
rcuos/6
8415062
schedule
schedule_hrtimeout_range_clock
schedule_hrtimeout_range
poll_schedule_timeout
do_select
core_sys_select
sys_select
entry_SYSCALL_64_fastpath
offcputime
8421478
schedule
worker_thread
kthread
ret_from_fork
kworker/4:0
8421492
schedule
schedule_hrtimeout_range_clock
schedule_hrtimeout_range
poll_schedule_timeout
do_select
core_sys_select
sys_select
entry_SYSCALL_64_fastpath
sshd
14249005
schedule
schedule_hrtimeout_range_clock
schedule_hrtimeout_range
poll_schedule_timeout
do_sys_poll
sys_poll
entry_SYSCALL_64_fastpath
supervise
81670888
Detaching...
The last few stack traces aren't very interesting, since they are threads that
are ofter blocked off-CPU waiting for work.
Do be somewhat careful with overhead: this is tracing scheduler functions, which
can be called very frequently. While this uses in-kernel summaries for
efficiency, the rate of scheduler functions can be very high (> 1,000,000/sec),
and this is performing stack walks when threads return to CPU. At some point
the overhead will be measurable.
A -p option can be used to filter (in-kernel) on a single process ID. For
example, only matching PID 26651, which is a running "dd" command:
# ./offcputime -p 26651
Tracing off-CPU time (us) by kernel stack... Hit Ctrl-C to end.
^C
schedule
schedule_timeout
io_schedule_timeout
do_blockdev_direct_IO
__blockdev_direct_IO
blkdev_direct_IO
generic_file_read_iter
blkdev_read_iter
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
dd
2405710
Detaching...
The stack trace shows "dd" is blocked waiting on disk I/O, as expected, for a
total of 2.4 seconds during tracing.
A duration can be added, for example, tracing for 5 seconds only:
# ./offcputime -p 26651 5
Tracing off-CPU time (us) by kernel stack for 5 secs.
schedule
schedule_timeout
io_schedule_timeout
do_blockdev_direct_IO
__blockdev_direct_IO
blkdev_direct_IO
generic_file_read_iter
blkdev_read_iter
__vfs_read
vfs_read
sys_read
entry_SYSCALL_64_fastpath
dd
4413909
Detaching...
Here, dd was blocked for 4.4 seconds out of 5. Or put differently, likely
on-CPU for about 12% of the time. Which matches the ratio seen by time(1):
# time dd if=/dev/md0 iflag=direct of=/dev/null bs=1k
^C108115+0 records in
108114+0 records out
110708736 bytes (111 MB) copied, 13.7565 s, 8.0 MB/s
real 0m13.760s
user 0m0.000s
sys 0m1.739s
A -f option will emit output using the "folded stacks" format, which can be
read directly by flamegraph.pl from the FlameGraph open source software
(https://github.com/brendangregg/FlameGraph). Eg:
# ./offcputime -f 5
bash;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;tty_read;n_tty_read;call_rwsem_down_read_failed;rwsem_down_read_failed;schedule 8
yes;entry_SYSCALL_64_fastpath;sys_write;vfs_write;__vfs_write;tty_write;n_tty_write;call_rwsem_down_read_failed;rwsem_down_read_failed;schedule 14
run;page_fault;do_page_fault;__do_page_fault;handle_mm_fault;__do_fault;filemap_fault;__lock_page_or_retry;wait_on_page_bit_killable;__wait_on_bit;bit_wait_io;io_schedule_timeout;schedule_timeout;schedule 33
rcuos/4;ret_from_fork;kthread;rcu_nocb_kthread;schedule 45
bash;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;pipe_read;pipe_wait;schedule 88
run;page_fault;do_page_fault;__do_page_fault;handle_mm_fault;__do_fault;filemap_fault;__lock_page_or_retry;wait_on_page_bit_killable;__wait_on_bit;bit_wait_io;io_schedule_timeout;schedule_timeout;schedule 108
jbd2/xvda1-8;mb_cache_list;ret_from_fork;kthread;kjournald2;jbd2_journal_commit_transaction;__wait_on_buffer;out_of_line_wait_on_bit;__wait_on_bit;bit_wait_io;io_schedule_timeout;schedule_timeout;schedule 828
jbd2/xvda1-8;mb_cache_list;ret_from_fork;kthread;kjournald2;jbd2_journal_commit_transaction;__wait_on_buffer;out_of_line_wait_on_bit;__wait_on_bit;bit_wait_io;io_schedule_timeout;schedule_timeout;schedule 6201
supervise;entry_SYSCALL_64_fastpath;sys_rename;dput;__dentry_kill;iput;evict;ext4_evict_inode;truncate_inode_pages_final;truncate_inode_pages_range;wait_on_page_bit;__wait_on_bit;bit_wait_io;io_schedule_timeout;schedule_timeout;schedule 41049
run;entry_SYSCALL_64_fastpath;sys_wait4;do_wait;schedule 120709
bash;entry_SYSCALL_64_fastpath;sys_wait4;do_wait;schedule 699320
ksoftirqd/0;ret_from_fork;kthread;smpboot_thread_fn;schedule 1077529
bash;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;tty_read;n_tty_read;wait_woken;schedule_timeout;schedule 1362045
sshd;entry_SYSCALL_64_fastpath;sys_select;core_sys_select;do_select;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule 1377627
migration/0;ddebug_tables;ret_from_fork;kthread;smpboot_thread_fn;schedule 2040753
snmpd;entry_SYSCALL_64_fastpath;sys_select;core_sys_select;do_select;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule 2197568
migration/5;ret_from_fork;kthread;smpboot_thread_fn;schedule 3079426
migration/7;ret_from_fork;kthread;smpboot_thread_fn;schedule 3084746
kworker/6:2;ret_from_fork;kthread;worker_thread;schedule 3940583
kworker/5:1;ret_from_fork;kthread;worker_thread;schedule 3944892
kworker/1:2;ret_from_fork;kthread;worker_thread;schedule 3999646
ntpd;entry_SYSCALL_64_fastpath;sys_select;core_sys_select;do_select;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule 3999904
kworker/u16:0;ret_from_fork;kthread;worker_thread;schedule 3999967
kworker/7:0;ret_from_fork;kthread;worker_thread;schedule 3999987
tail;entry_SYSCALL_64_fastpath;sys_nanosleep;hrtimer_nanosleep;do_nanosleep;schedule 4000473
migration/1;ret_from_fork;kthread;smpboot_thread_fn;schedule 4091150
migration/4;ret_from_fork;kthread;smpboot_thread_fn;schedule 4095217
readproctitle;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;pipe_read;pipe_wait;schedule 4108470
migration/3;ret_from_fork;kthread;smpboot_thread_fn;schedule 4109264
migration/2;ret_from_fork;kthread;smpboot_thread_fn;schedule 4109280
migration/6;ret_from_fork;kthread;smpboot_thread_fn;schedule 4111143
kworker/4:0;ret_from_fork;kthread;worker_thread;schedule 4402350
kworker/3:0;ret_from_fork;kthread;worker_thread;schedule 4433988
kworker/2:1;ret_from_fork;kthread;worker_thread;schedule 4636142
kworker/0:2;ret_from_fork;kthread;worker_thread;schedule 4832023
rcuos/1;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4974186
rcuos/5;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4977137
rcuos/6;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4987769
rcuos/3;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4992282
rcuos/4;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4992364
rcuos/2;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4992714
rcuos/0;ddebug_tables;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4996504
rcuos/7;ret_from_fork;kthread;rcu_nocb_kthread;schedule 4998497
rcu_sched;ddebug_tables;ret_from_fork;kthread;rcu_gp_kthread;schedule_timeout;schedule 5000686
offcputime;entry_SYSCALL_64_fastpath;sys_select;core_sys_select;do_select;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule 5005063
dd;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;blkdev_read_iter;generic_file_read_iter;blkdev_direct_IO;__blockdev_direct_IO;do_blockdev_direct_IO;io_schedule_timeout;schedule_timeout;schedule 8025599
supervise;entry_SYSCALL_64_fastpath;sys_poll;do_sys_poll;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule 40835611
The stack traces are shown as single lines, with functions separated by
semicolons. The first entry is the task name. The 2nd column is the total
off-CPU time.
I'd save this output to a file, then move it to the system where you'll be
creating your "off-CPU time flame graphs".
USAGE message:
# ./offcputime -h
usage: offcputime [-h] [-u] [-p PID] [-v] [-f] [duration]
Summarize off-CPU time by kernel stack trace
positional arguments:
duration duration of trace, in seconds
optional arguments:
-h, --help show this help message and exit
-u, --useronly user threads only (no kernel threads)
-p PID, --pid PID trace this PID only
-v, --verbose show raw addresses
-f, --folded output folded format
examples:
./offcputime # trace off-CPU stack time until Ctrl-C
./offcputime 5 # trace for 5 seconds only
./offcputime -f 5 # 5 seconds, and output in folded format
./offcputime -u # don't include kernel threads (user only)
./offcputime -p 185 # trace for PID 185 only