some bcc examples and tools
diff --git a/examples/vfsreadlat_example.txt b/examples/vfsreadlat_example.txt
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+Demonstrations of vfsreadlat.py, the Linux eBPF/bcc version.
+
+
+This example traces the latency of vfs_read (time from call to return), printing
+it as a histogram distribution. By default, output is every five seconds:
+
+# ./vfsreadlat.py
+Tracing... Hit Ctrl-C to end.
+
+ usecs : count distribution
+ 0 -> 1 : 4457 |*************************************+|
+ 2 -> 3 : 447 |*** |
+ 4 -> 7 : 2059 |***************** |
+ 8 -> 15 : 1179 |********** |
+ 16 -> 31 : 63 | |
+ 32 -> 63 : 0 | |
+ 64 -> 127 : 2 | |
+ 128 -> 255 : 0 | |
+ 256 -> 511 : 3 | |
+ 512 -> 1023 : 1 | |
+ 1024 -> 2047 : 3 | |
+ 2048 -> 4095 : 2 | |
+ 4096 -> 8191 : 0 | |
+ 8192 -> 16383 : 0 | |
+ 16384 -> 32767 : 0 | |
+ 32768 -> 65535 : 0 | |
+ 65536 -> 131071 : 4 | |
+ 131072 -> 262143 : 2 | |
+ 262144 -> 524287 : 0 | |
+ 524288 -> 1048575 : 4 | |
+^C
+ usecs : count distribution
+ 0 -> 1 : 241 |*************************************+|
+ 2 -> 3 : 17 |** |
+ 4 -> 7 : 2 | |
+ 8 -> 15 : 4 | |
+ 16 -> 31 : 2 | |
+ 32 -> 63 : 0 | |
+ 64 -> 127 : 1 | |
+ 128 -> 255 : 0 | |
+ 256 -> 511 : 1 | |
+ 512 -> 1023 : 1 | |
+ 1024 -> 2047 : 0 | |
+ 2048 -> 4095 : 1 | |
+ 4096 -> 8191 : 0 | |
+ 8192 -> 16383 : 0 | |
+ 16384 -> 32767 : 0 | |
+ 32768 -> 65535 : 0 | |
+ 65536 -> 131071 : 0 | |
+ 131072 -> 262143 : 0 | |
+ 262144 -> 524287 : 0 | |
+ 524288 -> 1048575 : 1 | |
+
+These examples show outliers in the 524 - 1048 milliseconds range. Since
+vfs_read() will catch many types of events, this could be anything including
+keystroke latency on ssh sessions. Further drilling with bcc will be necessary
+to identify more details.
+
+
+Full usage:
+
+# ./vfsreadlat.py -h
+USAGE: ./vfsreadlat.py [interval [count]]