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softirqs_example.txt
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softirqs_example.txt
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Demonstrations of softirqs, the Linux eBPF/bcc version.
This program traces soft interrupts (irqs), and stores timing statistics
in-kernel for efficiency. For example:
# ./softirqs
Tracing soft irq event time... Hit Ctrl-C to end.
^C
SOFTIRQ TOTAL_usecs
rcu_process_callbacks 974
run_rebalance_domains 1809
run_timer_softirq 2615
net_tx_action 14605
tasklet_action 38692
net_rx_action 88188
The SOFTIRQ column prints the interrupt action function name. While tracing,
the net_rx_action() soft interrupt ran for 20199 microseconds (20 milliseconds)
in total.
This tool works by dynamic tracing the individual softirq functions, and will
need to be adjusted to match kernel/module changes. Future versions should
use the softirq tracepoints instead.
An interval can be provided, and also optionally a count. Eg, printing output
every 1 second, and including timestamps (-T):
# ./softirqs -T 1 3
Tracing soft irq event time... Hit Ctrl-C to end.
22:29:16
SOFTIRQ TOTAL_usecs
rcu_process_callbacks 456
run_rebalance_domains 1005
run_timer_softirq 1196
net_tx_action 2796
tasklet_action 5534
net_rx_action 15075
22:29:17
SOFTIRQ TOTAL_usecs
rcu_process_callbacks 456
run_rebalance_domains 839
run_timer_softirq 1142
net_tx_action 1912
tasklet_action 4428
net_rx_action 14652
22:29:18
SOFTIRQ TOTAL_usecs
rcu_process_callbacks 502
run_rebalance_domains 840
run_timer_softirq 1192
net_tx_action 2341
tasklet_action 5496
net_rx_action 15656
This can be useful for quantifying where CPU cycles are spent among the soft
interrupts (summarized as the %softirq column from mpstat(1), and shown as
event counts in /proc/softirqs). The output above shows that most time was spent
processing net_rx_action(), which was around 15 milliseconds per second (total
time across all CPUs).
The distribution of interrupt run time can be printed as a histogram with the -d
option. Eg:
# ./softirqs -d
Tracing soft irq event time... Hit Ctrl-C to end.
^C
softirq = net_tx_action
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 440 | |
512 -> 1023 : 27613 |****************************************|
1024 -> 2047 : 5728 |******** |
2048 -> 4095 : 439 | |
4096 -> 8191 : 53 | |
8192 -> 16383 : 2 | |
softirq = net_rx_action
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 6 | |
1024 -> 2047 : 35 | |
2048 -> 4095 : 3562 |**************** |
4096 -> 8191 : 7023 |******************************** |
8192 -> 16383 : 8770 |****************************************|
16384 -> 32767 : 1780 |******** |
32768 -> 65535 : 216 | |
65536 -> 131071 : 4 | |
softirq = tasklet_action
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 95 | |
512 -> 1023 : 12521 |****************************************|
1024 -> 2047 : 1068 |*** |
2048 -> 4095 : 1077 |*** |
4096 -> 8191 : 12349 |*************************************** |
8192 -> 16383 : 464 |* |
16384 -> 32767 : 1 | |
softirq = rcu_process_callbacks
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 708 |****************************************|
1024 -> 2047 : 495 |*************************** |
2048 -> 4095 : 98 |***** |
4096 -> 8191 : 62 |*** |
8192 -> 16383 : 4 | |
softirq = run_timer_softirq
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 2 | |
512 -> 1023 : 366 |********* |
1024 -> 2047 : 1525 |****************************************|
2048 -> 4095 : 629 |**************** |
4096 -> 8191 : 87 |** |
8192 -> 16383 : 1 | |
softirq = run_rebalance_domains
usecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 3 | |
512 -> 1023 : 18 |* |
1024 -> 2047 : 80 |******** |
2048 -> 4095 : 374 |****************************************|
4096 -> 8191 : 257 |*************************** |
8192 -> 16383 : 50 |***** |
16384 -> 32767 : 24 |** |
USAGE message:
# ./softirqs -h
usage: softirqs [-h] [-T] [-N] [-d] [interval] [count]
Summarize soft irq event time as histograms
positional arguments:
interval output interval, in seconds
count number of outputs
optional arguments:
-h, --help show this help message and exit
-T, --timestamp include timestamp on output
-N, --nanoseconds output in nanoseconds
-d, --dist show distributions as histograms
examples:
./softirqs # sum soft irq event time
./softirqs -d # show soft irq event time as histograms
./softirqs 1 10 # print 1 second summaries, 10 times
./softirqs -NT 1 # 1s summaries, nanoseconds, and timestamps