On Thu, Apr 30, 2015 at 7:31 AM, Peter van Hooft <hooft at natlab.research.philips.com> wrote: >> You may want to try reducing sunrpc.tcp_max_slot_table_entries . >> In CentOS 5 the number of slots is fixed: sunrpc.tcp_slot_table_entries = 16 >> In CentOS 6, this number is dynamic with a maximum of >> sunrpc.tcp_max_slot_table_entries which by default has a value of 65536. >> >> We put that in /etc/sysconfig/modprobe.d/sunrpc.conf: options sunrpc >> tcp_max_slot_table_entries=128 > > Make that /etc/modprobe.d/sunrpc.conf, of course. This appears to be the "smoking gun" we were looking for, or at least a significant piece of the puzzle. We actually tried this early on in our investigation, but were changing it via sysctl, which apparently has no effect. Your email convinced me to try again, but this time configuring the parameters via modprobe. In our case, 128 was still too high. So we dropped it all the way down to 16. Our understanding is that 16 is the CentOS 5 value. What we're seeing is now our apps are starved for data, so looks like we might have to nudge it up. In other words, there's either something else at play which we're not aware of, or the meaning of that parameter is different between CentOS 5 and CentOS 6. Anyway, thank you very much for the suggestion. You turned on the light at the end of the tunnel!