btt: Added in I/O activity per device and system-wide

It now keeps track of I/O activity on a per-device basis (as well as a
cumulative system-wide view). ``I/O activity'' is defined as defined as
the time during which the device driver and device are activelty working
on at least one I/O. Here's a sample output:

==================== I/O Active Period Information ====================

       DEV |     # Live      Avg. Act     Avg. !Act % Live
---------- | ---------- ------------- ------------- ------
 (254,  0) |          0   0.000000000   0.000000000   0.00
 (  8, 17) |          0   0.000000000   0.000000000   0.00
 (  8, 16) |         29   0.909596815   0.094646263  90.87
 (  8, 33) |          0   0.000000000   0.000000000   0.00
 (  8, 32) |        168   0.097848226   0.068231948  59.06
---------- | ---------- ------------- ------------- ------
 Total Sys |         33   0.799808811   0.082334758  90.92

Also added a new btt -Z option that generates per-device and system-wide
I/O activity data that can be plotted.

Refer to the documentation updates (btt.1, btt.tex) for more information.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/btt.1 b/doc/btt.1
index b9c9ee7..60d28ac 100644
--- a/doc/btt.1
+++ b/doc/btt.1
@@ -59,6 +59,8 @@ btt \- analyse block i/o traces produces by blktrace
 [ \-V               | \-\-version ]
 .br
 [ \-z <\fIoutput name\fR> | \-\-q2d\-latencies=<\fIoutput name\fR> ]
+.br
+[ \-Z               | \-\-do\-active ]
 
 
 .SH DESCRIPTION
@@ -339,6 +341,14 @@ respectively. The supplied argument provides the basis for the output
 name for each device.
 .RE
 
+.B \-Z
+.br
+.B \-\-do\-active
+.RS 4
+The \-Z will output files containing data which can be plotted showing
+per\-device (and total system) I/O activity.
+.RE
+
 
 .SH AUTHORS
 \fIbtt\fR was written by Alan D. Brunelle.  This man page was created