make bitehist a simpler example of log2 histograms

examples/bitehist.py

@@ -5,8 +5,6 @@
 #
 # Written as a basic example of using a histogram to show a distribution.
 #
-# USAGE: bitehist.py [interval [count]]
-#
 # The default interval is 5 seconds. A Ctrl-C will print the partially
 # gathered histogram then exit.
 #
@@ -17,24 +15,6 @@
 
 from bcc import BPF
 from time import sleep
-from sys import argv
-
-def usage():
-	print("USAGE: %s [interval [count]]" % argv[0])
-	exit()
-
-# arguments
-interval = 5
-count = -1
-if len(argv) > 1:
-	try:
-		interval = int(argv[1])
-		if interval == 0:
-			raise
-		if len(argv) > 2:
-			count = int(argv[2])
-	except:	# also catches -h, --help
-		usage()
 
 # load BPF program
 b = BPF(src_file = "bitehist.c")
@@ -44,20 +24,10 @@ b.attach_kprobe(event="blk_start_request", fn_name="do_request")
 print("Tracing... Hit Ctrl-C to end.")
 
 # output
-loop = 0
-do_exit = 0
-while (1):
-	if count > 0:
-		loop += 1
-		if loop > count:
-			exit()
-	try:
-		sleep(interval)
-	except KeyboardInterrupt:
-		pass; do_exit = 1
-
+try:
+	sleep(99999999)
+except KeyboardInterrupt:
 	print
-	b["dist"].print_log2_hist()
-	b["dist"].clear()
-	if do_exit:
-		exit()
+
+b["dist"].print_log2_hist()
+b["dist"].clear()

examples/bitehist_example.txt

 Demonstrations of bitehist.py, the Linux eBPF/bcc version.
 
 This prints a power-of-2 histogram to show the block I/O size distribution.
-By default, a summary is printed every five seconds:
+A summary is printed after Ctrl-C is hit.
 
 # ./bitehist.py 
 Tracing... Hit Ctrl-C to end.
-
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
-       2 -> 3        : 0        |                                      |
-       4 -> 7        : 26       |*************                         |
-       8 -> 15       : 3        |*                                     |
-      16 -> 31       : 5        |**                                    |
-      32 -> 63       : 6        |***                                   |
-      64 -> 127      : 7        |***                                   |
-     128 -> 255      : 75       |**************************************|
-
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
-       2 -> 3        : 0        |                                      |
-       4 -> 7        : 83       |**************************************|
-       8 -> 15       : 2        |                                      |
-      16 -> 31       : 6        |**                                    |
-      32 -> 63       : 6        |**                                    |
-      64 -> 127      : 5        |**                                    |
-     128 -> 255      : 21       |*********                             |
 ^C
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
-       2 -> 3        : 0        |                                      |
-       4 -> 7        : 8        |**************************************|
-
-The first output shows a bimodal distribution. The largest mode of 75 I/O were
-between 128 and 255 Kbytes in size, and another mode of 26 I/O were between 4
-and 7 Kbytes in size. 
-
-The next output summary shows the workload is doing more 4 - 7 Kbyte I/O.
-
-The final output is partial, showing what was measured until Ctrl-C was hit.
-
-
-For an output interval of one second, and three summaries:
-
-# ./bitehist.py 1 3
-Tracing... Hit Ctrl-C to end.
-
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
+     value           : count     distribution
+       0 -> 1        : 3        |                                      |
        2 -> 3        : 0        |                                      |
-       4 -> 7        : 4        |**************************************|
-
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
-       2 -> 3        : 0        |                                      |
-       4 -> 7        : 5        |**************************************|
+       4 -> 7        : 211      |**********                            |
        8 -> 15       : 0        |                                      |
       16 -> 31       : 0        |                                      |
-      32 -> 63       : 1        |*******                               |
-
-     kbytes          : count     distribution
-       0 -> 1        : 0        |                                      |
-       2 -> 3        : 0        |                                      |
-       4 -> 7        : 4        |**************************************|
-
+      32 -> 63       : 0        |                                      |
+      64 -> 127      : 1        |                                      |
+     128 -> 255      : 800      |**************************************|
 
-Full usage:
+This output shows a bimodal distribution. The largest mod of 800 I/O were
+between 128 and 255 Kbytes in size, and another mode of 211 I/O were between
+4 and 7 Kbytes in size.
 
-# ./bitehist.py -h
-USAGE: ./bitehist.py [interval [count]]
+Understanding this distribution is useful for characterizing workloads and
+understanding performance. The existance of this distribution is not visible
+from averages alone.