[ntp:questions] Test ntpd performance

Rick Jones rick.jones2 at hp.com
Tue Sep 28 17:07:32 UTC 2010

Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:

> >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.

> Is that sending 1 byte of data per packet, or batching up
> several/many bytes per packet?  (and mostly measuring the CPU time
> for a one byte send/recv pair)

I seek to avoid batching by setting TCP_NODELAY on the socket and then
do spoit-checks on the link-level packet counts.

> Even if you have a test program that blasts lots of packets, that
> won't mimmic real traffic.  It's bypassing all the setup of ARP and
> router slots.

I'm not quite sure if I'm parsing that accurately - yes, such a
single-connection test between a pair of systems isn't doing much
to/with the ARP cache or routing tables, which means that if anything
for the 100000 client case the 350K transactions per second is
optimistic (*).  I should have been more clear - my main intent was to
show/suggest that the server could very likely indeed bottleneck
before a 1GbE link could.  Sort of an inverted (term?) "New York, New
York" (the song argument) where "If you can't make it there, you won't
make it anywhere" where netperf is "there" and the ntpd would be

rick jones

* then again, I'd hope there aren't 100000 clients in the same
broadcast domain, which suggests (ok, yes, I'm extrapolating) that
almost all the clients will be reached by the ntp server via its
default route, and thus also have only one active ARP cache entry -
much like the single-connection netperf test between systems on the
same LAN.

firebug n, the idiot who tosses a lit cigarette out his car window
these opinions are mine, all mine; HP might not want them anyway... :)
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