new benchmark framework

[Martin Hunt <hunt@redhat.com>]

I've checked in a new benchmark framework that makes it easy to see how
fast a code fragment is running. I've also got some simple tests
included.

Code is in src/runtime/bench2. It is self-contained and can be moved
anywhere. It uses the installed systemtap.

To write a test, simply create a file and put the following two lines at
the top:

---
#!/usr/bin/env ruby
load './bench.rb'

#Then create a test like this:

# script test to print 5 integers
test4 = Stapbench.new("printf 5 integers")
test4.code = "printf(\"%d, %d, %d, %d, %d\\n\", 1, 0xffff, 0x8000ffff,
0xffff000011112222, 0x7000000000000000)"
test4.run
test4.print
---

Then run the above file. That's it. 

It can test C code as well as Systemtap script. See the examples.

Sample output from "run_bench":

SystemTap BENCH2        Wed Mar 15 01:00:52 PST 2006
kernel: 2.6.9-34.ELsmp x86_64
Red Hat Enterprise Linux WS release 4 (Nahant Update 3)
tiger:  01:00:52 up 51 min,  1 user,  load average: 1.46, 1.29, 0.87
processors: 4 (2 physical)                   Intel(R) Xeon(TM) CPU
2.80GHz
MemTotal:      1025428 kB       MemFree:        750220 kB
----------------------------------------------------------------
For comparison, function call overhead is 721 nsecs.
Times below are nanoseconds per probe and include kprobe overhead.
----------------------------------------------------------------
+--- S = Script, R = Runtime
|+-- * = Relayfs                Threads
|| NAME                         1       2       4
R : empty probe                 1471    737     559
S : empty probe                 1556    784     594
S : printf 100 chars            2178    1445    1148
S*: printf 100 chars            2184    1290    1108
R : printf 100 chars            2064    1333    1039
R : printf 5 integers           3793    2006    1589
S : printf 5 integers           3930    2136    1644

You can see the overhead for printing integers is high. We should be
able to improve on all the printf numbers soon.

Martin