Subj : Re: Solaris real-time thread capabilities
To   : comp.unix.solaris,comp.programming.threads
From : Greg Menke
Date : Sat Sep 03 2005 12:52 am


Until you measure your application scheduling with a hires timer, you
have no idea where the jitter is coming from.

IP does not guarantee you realtime transfer of data- or even reasonably
bounded latency.  Its not clear what your "packages" are or how you're
transferring them, so I assume you're sending packets via UDP.  If
you're sending them via TCP, you have even bigger problems.

An IP stack can easily add 10's of milliseconds to some packets and not
others, or it will plain drop them with no notification to you.  This
often leads people to try TCP, which can, will and invisibly adds all
kinds of delays you cannot control or even observe.

You should not be relying on a network for realtime transfers until &
unless you have something like a TDMA stack, driver and phy layer and
your app is designed to use it.  Even if the operating systems and IP
stacks on both end of the transfer offer some form of bounded latency,
your comms timing is then wholly dependent on how much latency
intervening switches & routers add, which to a considerable degree
depends on ambient traffic which is still more random.

You might be able to get around it by doing your realtime sampling in
one task, then accumulating timestamped data in a 2nd regular priority
task which handles transfers to the destination machine.

It sounds to me as if you have not designed your system to handle
real-world characteristics of computers and networks.

Gregm

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