FM / examples

/usr/share/doc/bpftrace/examples

Name	Size	Mode	Actions
bashreadline_example.txt	722	0644	edit dl rm
biolatency_example.txt	1790	0644	edit dl rm
biosnoop_example.txt	2056	0644	edit dl rm
biostacks_example.txt	1914	0644	edit dl rm
bitesize_example.txt	3003	0644	edit dl rm
capable_example.txt	2659	0644	edit dl rm
cpuwalk_example.txt	4919	0644	edit dl rm
dcsnoop_example.txt	4612	0644	edit dl rm
execsnoop_example.txt	1535	0644	edit dl rm
gethostlatency_example.txt	923	0644	edit dl rm
killsnoop_example.txt	846	0644	edit dl rm
loads_example.txt	864	0644	edit dl rm
mdflush_example.txt	1866	0644	edit dl rm
naptime_example.txt	844	0644	edit dl rm
oomkill_example.txt	1668	0644	edit dl rm
opensnoop_example.txt	2528	0644	edit dl rm
pidpersec_example.txt	1504	0644	edit dl rm
runqlat_example.txt	8632	0644	edit dl rm
runqlen_example.txt	980	0644	edit dl rm
setuids_example.txt	2441	0644	edit dl rm
ssllatency_example.txt	4510	0644	edit dl rm
sslsnoop_example.txt	1916	0644	edit dl rm
statsnoop_example.txt	2738	0644	edit dl rm
swapin_example.txt	549	0644	edit dl rm
syncsnoop_example.txt	541	0644	edit dl rm
syscount_example.txt	1144	0644	edit dl rm
tcpaccept_example.txt	1350	0644	edit dl rm
tcpconnect_example.txt	1085	0644	edit dl rm
tcpdrop_example.txt	1256	0644	edit dl rm
tcplife_example.txt	1597	0644	edit dl rm
tcpretrans_example.txt	1153	0644	edit dl rm
tcpsynbl_example.txt	940	0644	edit dl rm
threadsnoop_example.txt	1182	0644	edit dl rm
undump_example.txt	680	0644	edit dl rm
vfscount_example.txt	1199	0644	edit dl rm
vfsstat_example.txt	929	0644	edit dl rm
writeback_example.txt	1962	0644	edit dl rm
xfsdist_example.txt	3419	0644	edit dl rm

Edit: /usr/share/doc/bpftrace/examples/writeback_example.txt (1962B)

Demonstrations of writeback, the Linux bpftrace/eBPF version.

This tool traces when the kernel writeback procedure is writing dirtied pages
to disk, and shows details such as the time, device numbers, reason for the
write back, and the duration. For example:

# ./writeback.bt
Attaching 4 probes...
Tracing writeback... Hit Ctrl-C to end.
TIME      DEVICE   PAGES    REASON           ms
23:28:47  259:1    15791    periodic         0.005
23:28:48  259:0    15792    periodic         0.004
23:28:52  259:1    15784    periodic         0.003
23:28:53  259:0    18682    periodic         0.003
23:28:55  259:0    41970    background       326.663
23:28:56  259:0    18418    background       332.689
23:28:56  259:0    60402    background       362.446
23:28:57  259:1    18230    periodic         0.005
23:28:57  259:1    65492    background       3.343
23:28:57  259:1    65492    background       0.002
23:28:58  259:0    36850    background       0.000
23:28:58  259:0    13298    background       597.198
23:28:58  259:0    55282    background       322.050
23:28:59  259:0    31730    background       336.031
23:28:59  259:0    8178     background       357.119
23:29:01  259:0    50162    background       1803.146
23:29:02  259:0    27634    background       1311.876
23:29:03  259:0    6130     background       331.599
23:29:03  259:0    50162    background       293.968
23:29:03  259:0    28658    background       284.946
23:29:03  259:0    7154     background       286.572
[...]

By looking a the timestamps and latency, it can be seen that the system was
not spending much time in writeback until 23:28:55, when "background"
writeback began, taking over 300 milliseconds per flush.

If timestamps of heavy writeback coincide with times when applications suffered
performance issues, that would be a clue that they are correlated and there
is contention for the disk devices. There are various ways to tune this:
eg, vm.dirty_writeback_centisecs.

cmd: