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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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