I have a jboss process that uses JCA to do IO. So basically Jboss application thread sends a raw binary data to the external process. This external process that runs on the same linux box then converts it into a different format. Average size of this raw payload is 100K and post processed size is 100bytes. Normal conversion rates are 4/sec when I am sending 6 transactions / sec. When I double the transaction from 6/sec to 12/sec the conversion rates fall to 2/sec. I am assuming it has something to do with IO but I am not sure what exactly I can do to pinpoint real cause. I've looked at iostat output but didn't find anything there. iostat output:

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
cciss/c0d0 0.00 173.50 0.00 24.00 0.00 1580.00 0.00 790.00 65.83 0.41 17.15 6.31 15.15