Our performance tests show that ISC BIND (authoritative only setup) doesn't
perform well on RHEL 6.4 in comparison with FreeBSD 7: bind_perf.png
bind_perf.png
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The "Drop Rate" is the ratio of the amount response never received and the
amount of requests were sent. BIND is configured with 24 worker threads and 24
UPD listener, same as the CPU threads we have. BIND process already has '-20'
nice priority set on RHEL and '20' on the FreeBSD host.The test hosts running
RHEL 6.4 and FreeBSD 7 are identical in term of hardware:
2 x Xeon E5-2430, 24GB DDR3 RAM, 1Gb/s NIC.
We conducted the tests by having our load generators re-play BIND query logs
using our custom scripts and send the queries to the test server at a given
rate, say, 200,00 query per seconds. The queries are preloaded into the memory
so that's no overhead for our load generators to read queries from disk while
sending test queries.
What we've observed that socket receiving queue (Recv-Q from netstat) drained
very fast on FreeBSD but got back up pretty fast on RHEL 6 when we ramped up
the test traffic. With net.core.rmem_default set to 40MB, it only helps RHEL
to be able to handle 180,000qps before we start to see receive buffer overruns
again and drop rate increases linearly.
We are using governor performance on RHEL because default governor ondemand
really hurts performance.
vmstat output gathered from RHEL and FreeBSD hosts showed that FreeBSD is
scheduling those BIND threads more efficiently than RHEL as the number of
running processes is quite stable on FreeBSD and context switches/interrupts
ratio is lower and user space CPU utilization is better than RHEL. The below
links showed vmstat gathered with 1-second interval during the test run (200k
qps) which lasted for about 60 seconds.
vmstat_from_freebsd.txt
vmstat_from_freebsd.txt
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vmstat_from_rhel6.txt
vmstat_from_rhel6.txt
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Anyone has ideas on how to tune the scheduler on RHEL6 to work better for BIND?
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