Demonstrations of btrfsslower, the Linux eBPF/bcc version. btrfsslower shows btrfs reads, writes, opens, and fsyncs, slower than a threshold. For example: # ./btrfsslower Tracing btrfs operations slower than 10 ms TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 01:22:03 randread.pl 13602 R 8192 391384 10.40 data1 01:22:03 randread.pl 13602 R 8192 92632 10.41 data1 01:22:06 randread.pl 13602 R 8192 199800 17.33 data1 01:22:06 randread.pl 13602 R 8192 415160 17.21 data1 01:22:07 randread.pl 13602 R 8192 729984 11.93 data1 01:22:09 randread.pl 13602 R 8192 342784 11.90 data1 [...] This shows several reads from a "randread.pl" program, each 8 Kbytes in size, and from a "data1" file. These all had over 10 ms latency. This "latency" is measured from when the operation was issued from the VFS interface to the file system, to when it completed. This spans everything: block device I/O (disk I/O), file system CPU cycles, file system locks, run queue latency, etc. This is a better measure of the latency suffered by applications reading from the file system than measuring this down at the block device interface. Note that this only traces the common file system operations previously listed: other file system operations (eg, inode operations including getattr()) are not traced. The threshold can be provided as an argument. Eg, I/O slower than 1 ms: # ./btrfsslower 1 Tracing btrfs operations slower than 1 ms TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 03:26:54 randread.pl 30578 R 8192 214864 1.87 data1 03:26:54 randread.pl 30578 R 8192 267600 1.48 data1 03:26:54 randread.pl 30578 R 8192 704200 1.30 data1 03:26:54 randread.pl 30578 R 8192 492352 3.09 data1 03:26:55 randread.pl 30578 R 8192 319448 1.34 data1 03:26:55 randread.pl 30578 R 8192 676032 1.88 data1 03:26:55 randread.pl 30578 R 8192 646712 2.24 data1 03:26:55 randread.pl 30578 R 8192 124376 1.02 data1 03:26:55 randread.pl 30578 R 8192 223064 2.64 data1 03:26:55 randread.pl 30578 R 8192 521280 1.55 data1 03:26:55 randread.pl 30578 R 8192 272992 2.48 data1 03:26:55 randread.pl 30578 R 8192 450112 2.67 data1 03:26:55 randread.pl 30578 R 8192 361808 1.78 data1 03:26:55 randread.pl 30578 R 8192 41088 1.46 data1 03:26:55 randread.pl 30578 R 8192 756576 1.67 data1 03:26:55 randread.pl 30578 R 8192 711776 2.74 data1 03:26:55 randread.pl 30578 R 8192 129472 1.34 data1 03:26:55 randread.pl 30578 R 8192 526928 1.82 data1 03:26:56 randread.pl 30578 R 8192 312768 1.44 data1 03:26:56 randread.pl 30578 R 8192 34720 1.14 data1 03:26:56 randread.pl 30578 R 8192 258376 1.13 data1 03:26:56 randread.pl 30578 R 8192 308456 1.44 data1 03:26:56 randread.pl 30578 R 8192 759656 1.27 data1 03:26:56 randread.pl 30578 R 8192 387424 3.24 data1 03:26:56 randread.pl 30578 R 8192 168864 3.38 data1 03:26:56 randread.pl 30578 R 8192 699296 1.38 data1 03:26:56 randread.pl 30578 R 8192 405688 2.37 data1 03:26:56 randread.pl 30578 R 8192 559064 1.18 data1 03:26:56 randread.pl 30578 R 8192 264808 1.13 data1 03:26:56 randread.pl 30578 R 8192 369240 2.20 data1 [...] There's now much more output (this spans less than 3 seconds, the previous output spanned 6 seconds), as the lower threshold is catching more I/O. A threshold of 0 will trace all operations. Warning: the output will be verbose, as it will include all file system cache hits. # ./btrfsslower 0 Tracing btrfs operations TIME COMM PID T BYTES OFF_KB LAT(ms) FILENAME 03:28:17 bash 32597 O 0 0 0.00 date.txt 03:28:17 date 32597 W 29 0 0.02 date.txt 03:28:23 cksum 32743 O 0 0 0.00 date.txt 03:28:23 cksum 32743 R 29 0 0.01 date.txt 03:28:23 cksum 32743 R 0 0 0.00 date.txt While tracing, the following commands were run in another window: # date > date.txt # cksum date.txt The output of btrfsslower now includes open operations ("O"), and writes ("W"). The first read from cksum(1) returned 29 bytes, and the second returned 0: causing cksum(1) to stop reading. A -j option will print just the fields (parsable output, csv): # ./btrfsslower -j 1 ENDTIME_us,TASK,PID,TYPE,BYTES,OFFSET_b,LATENCY_us,FILE 8930665366,randread.pl,2717,R,8192,230391808,4312,data1 8930670746,randread.pl,2717,R,8192,347832320,1296,data1 8930675995,randread.pl,2717,R,8192,409812992,4207,data1 8930680213,randread.pl,2717,R,8192,498204672,3104,data1 8930685970,randread.pl,2717,R,8192,553164800,1843,data1 8930687568,randread.pl,2717,R,8192,339492864,1475,data1 8930694108,randread.pl,2717,R,8192,500711424,6276,data1 8930697139,randread.pl,2717,R,8192,485801984,2180,data1 8930705755,randread.pl,2717,R,8192,376922112,7535,data1 8930711340,randread.pl,2717,R,8192,380084224,3314,data1 8930740964,randread.pl,2717,R,8192,226091008,24762,data1 8930743169,randread.pl,2717,R,8192,361570304,1809,data1 8930748789,randread.pl,2717,R,8192,346931200,1530,data1 8930763514,randread.pl,2717,R,8192,59719680,13938,data1 8930764870,randread.pl,2717,R,8192,406511616,1313,data1 8930774327,randread.pl,2717,R,8192,661430272,7361,data1 8930780360,randread.pl,2717,R,8192,406904832,2220,data1 8930785736,randread.pl,2717,R,8192,523419648,2005,data1 8930794560,randread.pl,2717,R,8192,342974464,8388,data1 [...] This may be useful for visualizing with another tool, for example, for producing a scatter plot of ENDTIME vs LATENCY, to look for time-based patterns. USAGE message: # ./btrfsslower -h usage: btrfsslower [-h] [-j] [-p PID] [min_ms] Trace common btrfs file operations slower than a threshold positional arguments: min_ms minimum I/O duration to trace, in ms (default 10) optional arguments: -h, --help show this help message and exit -j, --csv just print fields: comma-separated values -p PID, --pid PID trace this PID only examples: ./btrfsslower # trace operations slower than 10 ms (default) ./btrfsslower 1 # trace operations slower than 1 ms ./btrfsslower -j 1 # ... 1 ms, parsable output (csv) ./btrfsslower 0 # trace all operations (warning: verbose) ./btrfsslower -p 185 # trace PID 185 only