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klockstat(8) System Manager's Manual klockstat(8)

NAME

klockstat - Traces kernel mutex lock events and display locks statistics. Uses Linux eBPF/bcc.

SYNOPSIS

klockstat [-h] [-i] [-n] [-s] [-c] [-S FIELDS] [-p] [-t] [-d DURATION]

DESCRIPTION

klockstat traces kernel mutex lock events and display locks statistics and displays following data:


Caller Avg Spin Count Max spin Total spin
psi_avgs_work+0x2e 3675 5 5468 18379
flush_to_ldisc+0x22 2833 2 4210 5667
n_tty_write+0x30c 3914 1 3914 3914
isig+0x5d 2390 1 2390 2390
tty_buffer_flush+0x2a 1604 1 1604 1604
commit_echoes+0x22 1400 1 1400 1400
n_tty_receive_buf_common+0x3b9 1399 1 1399 1399


Caller Avg Hold Count Max hold Total hold
flush_to_ldisc+0x22 42558 2 76135 85116
psi_avgs_work+0x2e 14821 5 20446 74106
n_tty_receive_buf_common+0x3b9 12300 1 12300 12300
n_tty_write+0x30c 10712 1 10712 10712
isig+0x5d 3362 1 3362 3362
tty_buffer_flush+0x2a 3078 1 3078 3078
commit_echoes+0x22 3017 1 3017 3017

Every caller to using kernel's mutex is displayed on every line.

First portion of lines show the lock acquiring data, showing the amount of time it took to acquired given lock.


'Caller' - symbol acquiring the mutex
'Average Spin' - average time to acquire the mutex
'Count' - number of times mutex was acquired
'Max spin' - maximum time to acquire the mutex
'Total spin' - total time spent in acquiring the mutex

Second portion of lines show the lock holding data, showing the amount of time it took to hold given lock.


'Caller' - symbol holding the mutex
'Average Hold' - average time mutex was held
'Count' - number of times mutex was held
'Max hold' - maximum time mutex was held
'Total hold' - total time spent in holding the mutex

This works by tracing mutex_lock/unlock kprobes, updating the lock stats in maps and processing them in the python part.

Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

CONFIG_BPF and bcc.

OPTIONS

Print usage message.
print summary at this interval (seconds)
print locks taken by given caller filter (e.g., pipe_)
sort data on specific columns defined by FIELDS string (by default the data is sorted by Max columns)

FIELDS string contains 1 or 2 fields describing columns to sort on for both acquiring and holding data. Following fields are available:


acq_max for 'Max spin' column
acq_total for 'Total spin' column
acq_count for 'Count' column


hld_max for 'Max hold' column
hld_total for 'Total hold' column
hld_count for 'Count' column

See EXAMPLES.

print COUNT number of locks
print COUNT number of stack entries
Trace this process ID only (filtered in-kernel).
Trace this thread ID only (filtered in-kernel).
Total duration of trace in seconds.
Change the number of unique stack traces that can be stored and displayed.

EXAMPLES

# klockstat -S acq_count

# klockstat -S hld_total

# klockstat -S acq_count,hld_total

# klockstat

# klockstat -d 5

# klockstat -i 5

# klockstat -p 123

# klockstat -t 321

# klockstat -c pipe_

# klockstat -n 3

# klockstat -n 1 -s 10

Tracing lock events... Hit Ctrl-C to end. ^C
Caller Avg Spin Count Max spin Total spin
pipe_wait+0xa9 670 397691 17273 266775437
pipe_wait+0xa9
pipe_read+0x206
new_sync_read+0x12a
vfs_read+0x9d
ksys_read+0x5f
do_syscall_64+0x5b
entry_SYSCALL_64_after_hwframe+0x44


Caller Avg Hold Count Max hold Total hold
flush_to_ldisc+0x22 28381 3 65484 85144
flush_to_ldisc+0x22
process_one_work+0x1b0
worker_thread+0x50
kthread+0xfb
ret_from_fork+0x35

SOURCE

This is from bcc.

https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS

Linux

CREDITS

This tool is based on work of David Valin <dvalin@redhat.com> and his script.

AUTHOR

Jiri Olsa

2019-10-22 USER COMMANDS