1Demonstrations of klockstat, the Linux eBPF/bcc version. 2 3klockstat traces kernel mutex lock events and display locks statistics 4 5# klockstat.py 6Tracing lock events... Hit Ctrl-C to end. 7^C 8 Caller Avg Spin Count Max spin Total spin 9 psi_avgs_work+0x2e 3675 5 5468 18379 10 flush_to_ldisc+0x22 2833 2 4210 5667 11 n_tty_write+0x30c 3914 1 3914 3914 12 isig+0x5d 2390 1 2390 2390 13 tty_buffer_flush+0x2a 1604 1 1604 1604 14 commit_echoes+0x22 1400 1 1400 1400 15 n_tty_receive_buf_common+0x3b9 1399 1 1399 1399 16 17 Caller Avg Hold Count Max hold Total hold 18 flush_to_ldisc+0x22 42558 2 76135 85116 19 psi_avgs_work+0x2e 14821 5 20446 74106 20 n_tty_receive_buf_common+0x3b9 12300 1 12300 12300 21 n_tty_write+0x30c 10712 1 10712 10712 22 isig+0x5d 3362 1 3362 3362 23 tty_buffer_flush+0x2a 3078 1 3078 3078 24 commit_echoes+0x22 3017 1 3017 3017 25 26 27Every caller to using kernel's mutex is displayed on every line. 28 29First portion of lines show the lock acquiring data, showing the 30amount of time it took to acquired given lock. 31 32 'Caller' - symbol acquiring the mutex 33 'Average Spin' - average time to acquire the mutex 34 'Count' - number of times mutex was acquired 35 'Max spin' - maximum time to acquire the mutex 36 'Total spin' - total time spent in acquiring the mutex 37 38Second portion of lines show the lock holding data, showing the 39amount of time it took to hold given lock. 40 41 'Caller' - symbol holding the mutex 42 'Average Hold' - average time mutex was held 43 'Count' - number of times mutex was held 44 'Max hold' - maximum time mutex was held 45 'Total hold' - total time spent in holding the mutex 46 47This works by tracing mutex_lock/unlock kprobes, updating the 48lock stats in maps and processing them in the python part. 49 50 51An -i option can be used to display stats in interval (5 seconds in example below): 52 53# klockstat.py -i 5 54Tracing lock events... Hit Ctrl-C to end. 55 56 Caller Avg Spin Count Max spin Total spin 57 psi_avgs_work+0x2e 3822 15 5650 57338 58 flush_to_ldisc+0x22 4630 1 4630 4630 59 work_fn+0x4f 4185 1 4185 4185 60 61 Caller Avg Hold Count Max hold Total hold 62 psi_avgs_work+0x2e 12155 15 15739 182329 63 flush_to_ldisc+0x22 13809 1 13809 13809 64 work_fn+0x4f 5274 1 5274 5274 65 66 Caller Avg Spin Count Max spin Total spin 67 psi_avgs_work+0x2e 3715 17 4374 63163 68 69 Caller Avg Hold Count Max hold Total hold 70 psi_avgs_work+0x2e 13141 17 19510 223399 71^C 72 73 74A -p option can be used to trace only selected process: 75 76# klockstat.py -p 883 77Tracing lock events... Hit Ctrl-C to end. 78^C 79 Caller Avg Spin Count Max spin Total spin 80 pipe_wait+0xa9 625 412686 16930 258277958 81 pipe_read+0x3f 420 413425 16872 174017649 82 pipe_write+0x35 471 413425 16765 194792253 83 84 Caller Avg Hold Count Max hold Total hold 85 pipe_read+0x3f 473 413425 20063 195773647 86 pipe_wait+0xa9 604 412686 16972 249598153 87 pipe_write+0x35 481 413425 16944 199008064 88 89 90A -c option can be used to display only callers with specific substring: 91 92# klockstat.py -c pipe_ 93Tracing lock events... Hit Ctrl-C to end. 94^C 95 Caller Avg Spin Count Max spin Total spin 96 pipe_read+0x3f 422 469554 18665 198354705 97 pipe_wait+0xa9 679 469536 17196 319017069 98 pipe_write+0x35 469 469554 17057 220338525 99 100 Caller Avg Hold Count Max hold Total hold 101 pipe_write+0x35 638 469554 17330 299857180 102 pipe_wait+0xa9 779 469535 16912 366047392 103 pipe_read+0x3f 575 469554 13251 270005394 104 105 106An -n option can be used to display only specific number of callers: 107 108# klockstat.py -n 3 109Tracing lock events... Hit Ctrl-C to end. 110^C 111 Caller Avg Spin Count Max spin Total spin 112 pipe_read+0x3f 420 334120 16964 140632284 113 pipe_wait+0xa9 688 334116 16876 229957062 114 pipe_write+0x35 463 334120 16791 154981747 115 116 Caller Avg Hold Count Max hold Total hold 117 flush_to_ldisc+0x22 27754 3 63270 83264 118 pipe_read+0x3f 571 334120 17123 190976463 119 pipe_wait+0xa9 759 334115 17068 253747213 120 121 122An -s option can be used to display number of callers backtrace entries: 123 124# klockstat.py -n 1 -s 3 125Tracing lock events... Hit Ctrl-C to end. 126^C 127 Caller Avg Spin Count Max spin Total spin 128 pipe_wait+0xa9 685 811947 17376 556542328 129 pipe_wait+0xa9 130 pipe_read+0x206 131 132 Caller Avg Hold Count Max hold Total hold 133 flush_to_ldisc+0x22 28145 3 63872 84437 134 flush_to_ldisc+0x22 135 process_one_work+0x1b0 136 137 138Output can be sorted by using -S <fields> option on various 139fields, the acq_total will force the acquired table to be 140sorted on 'Total spin' column: 141 142# klockstat.py -S acq_total 143Tracing lock events... Hit Ctrl-C to end. 144^C 145 Caller Avg Spin Count Max spin Total spin 146 pipe_wait+0xa9 691 269343 17190 186263983 147 pipe_write+0x35 464 269351 11730 125205417 148 pipe_read+0x3f 422 269351 17107 113724697 149 psi_avgs_work+0x2e 2499 11 4454 27494 150 flush_to_ldisc+0x22 3111 3 5096 9334 151 n_tty_write+0x30c 2764 1 2764 2764 152 isig+0x5d 1287 1 1287 1287 153 tty_buffer_flush+0x2a 961 1 961 961 154 commit_echoes+0x22 892 1 892 892 155 n_tty_receive_buf_common+0x3b9 868 1 868 868 156 157 Caller Avg Hold Count Max hold Total hold 158 pipe_wait+0xa9 788 269343 17128 212496240 159 pipe_write+0x35 637 269351 17209 171596811 160 pipe_read+0x3f 585 269351 11834 157606323 161 psi_avgs_work+0x2e 8726 11 19177 95996 162 flush_to_ldisc+0x22 22158 3 43731 66474 163 n_tty_write+0x30c 9770 1 9770 9770 164 n_tty_receive_buf_common+0x3b9 6830 1 6830 6830 165 isig+0x5d 3114 1 3114 3114 166 tty_buffer_flush+0x2a 2032 1 2032 2032 167 commit_echoes+0x22 1616 1 1616 1616 168