[ntp:questions] Test ntpd performance
rick.jones2 at hp.com
Mon Sep 27 19:21:50 UTC 2010
unruh <unruh at wormhole.physics.ubc.ca> wrote:
> The dominant rate limiter is the network-- even if you have a 1Gb
> network-- switches, interrupts, etc.
Including a 14 byte Ethernet header, an NTP query/response appears to
be 80 bytes or 640 bits. The 1GbE interframe gap is allowed to be as
low as 64 bit times. So, call that 640+64 or 704 bits. That is a
maximum then of a little over 1.42 million queries per second (since
1GbE is full-duplex).
Now, I have seen aggregate netperf TCP_RR tests achieve in excess of
1.8M transactions (queries) per second over a 10GbE NIC, but never to
a single-threaded process. The 10GbE NIC I was using at the time did
have a low-ish PPS limit.
The most I've seen a single netperf *single-byte* burst-mode test do
is on the order of 350K transactions per second, and that is when
netperf is bound to a core other than the one taking interrupts from
the NIC to get some additional parallelism. In a netperf TCP_RR test,
netperf does virutally nothing but a send()/recv() pair and a couple
conditionals and adds.
Are there "multi-threaded" NTP server implementations? If not, I
suspect it is possible for an NTP server to saturate before the 1GbE
network to which it is connected.
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