Finally I able to configure and run this program on my 3 node cluster. 
#python stress.py -n 200000 -t 200  -d 172.16.7.76,172.16.7.77,172.16.7.78  -o read
total,interval_op_rate,avg_latency,elapsed_time
83664,8366,0.0278478825376,10
145478,6181,0.0295496694395,20
177409,3193,0.027055770029,30
200000,2259,0.0238709857141,40
#

I understand that this tool prints summary results for every 10 seconds.
total,interval_op_rate,avg_latency,elapsed_time
83664,8366,0.0278478825376,10

83664 reads  in first 10 seconds,  i.e  8366 TPS ( matching with interval_op_rate)
I am not able understand  exact meaning of  avg_latency field , how it calculates this average latency.

83664 operations took 10 secs,  so average value for one operation should be (10*1000)/83664 =  0.1195 ms.

I appreciate any information on avg_latency description?

Thanks,
Sam.





#python stress.py -n 200000 -t 200  -d 172.16.7.76,172.16.7.77,172.16.7.78  -o read
total,interval_op_rate,avg_latency,elapsed_time
83664,8366,0.0278478825376,10
145478,6181,0.0295496694395,20
177409,3193,0.027055770029,30
200000,2259,0.0238709857141,40





From: Peter Schuller <peter.schuller@infidyne.com>
To: user@cassandra.apache.org
Sent: Wed, August 4, 2010 6:51:53 PM
Subject: Re: stress.py

> After I add the thift libs to CLASS_PATH , it's failing with following
> error.
>
> /stress.py: line 21: have_multiproc: command not found
> ./stress.py: line 22: try:: command not found

And that sounds like stress.py is being run by a shell rather than by
Python. Not sure how that happened since stress.py has a proper
shebang, including in cassandra 0.6.3.

Are you running it with 'python'? Is this an old cassandra that maybe
didn't have a shebang in it's py_stress (I don't know, grasping at
straws)?

--
/ Peter Schuller