Current File : //usr/share/systemtap/examples/lwtools/fsslower-nd_example.txt
Examples of fsslower-nd.stp, the Linux SystemTap version.
This tool prints event-by-event details for each file system synchronous read
or write slower than a threshold. It works by dynamically traces two common
file system functions: do_sync_read() and do_sync_write(). Many, but not all,
file systems and workloads use these functions. Tracing their time provides one
view of suffered file system latency.
Tracing FS sync reads and writes slower than 5 ms:
# ./fsslower-nd.stp 5
Tracing FS sync reads and writes slower than 5 ms... Hit Ctrl-C to end.
TIME PID COMM FUNC SIZE LAT(ms)
22:27:28 2346 randread.pl do_sync_read 8192 11
22:27:28 2346 randread.pl do_sync_read 8192 14
22:27:28 2346 randread.pl do_sync_read 8192 6
22:27:28 2346 randread.pl do_sync_read 8192 5
22:27:28 2346 randread.pl do_sync_read 8192 6
22:27:28 2346 randread.pl do_sync_read 8192 5
22:27:28 2346 randread.pl do_sync_read 8192 24
22:27:28 2346 randread.pl do_sync_read 8192 12
22:27:28 2346 randread.pl do_sync_read 8192 9
22:27:28 2346 randread.pl do_sync_read 8192 9
22:27:28 2346 randread.pl do_sync_read 8192 5
22:27:28 2346 randread.pl do_sync_read 8192 8
22:27:28 2346 randread.pl do_sync_read 8192 14
22:27:28 2346 randread.pl do_sync_read 8192 10
22:27:28 2346 randread.pl do_sync_read 8192 6
22:27:28 2346 randread.pl do_sync_read 8192 5
[...]
This shows that the randread.pl process was suffering latency up to 26 ms, when
issuing do_sync_read()s of 8 Kbytes.
As this is designed to be a non-debuginfo tool, there are not that many details
available. Investigate further using other tools and custom SystemTap.
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