stddev
Stores the standard deviation of the specified expressions in an aggregation.
void stddev(expr)The stddev function is an aggregation function that returns the standard
deviation for an expression.
The standard deviation is imprecisely approximated as
√((Σ(x2)/N)-(Σx/N)2). This value is sufficient
for most DTrace purposes.
Example 8-47 How to use stddev to display the standard deviation of time taken to run processes
The example stores the timestamp for the syscall::execve:entry probe fires
and then subtracts this value from the timestamp when the
syscall::execve:return fires. The standard deviation is calculated based
on the time difference between the two probes and stored in an aggregation so that it can be
updated for each process that runs. When the program exits, the aggregated standard
deviation value is displayed.
syscall::execve:entry
{
self->ts = timestamp;
}
syscall::execve:return
/ self->ts /
{
t = timestamp - self->ts;
@execsd[execname] = stddev(t);
self->ts = 0;
}
END
{
printf("\nSTDDEV:");
printa(@execsd);
}Output similar to the following is displayed when the program exits:
STDDEV:
head 0
lsb_release 0
mkdir 0
pidof 0
pkla-check-auth 0
tr 0
uname 0
getopt 5646
basename 7061
sed 7236