RE: Socket Listener Delay Issue

I believe the hardware and OS are doing what they're designed to do.

IBMi and Power Systems are designed to be a multiple user environment and do not facilitate quick response to what would be interrupts on an Intel architecture. Events like a socket connection are handled within a priority structure that guarantees delivery of the event, but does not guarantee "real time" delivery. Events are queued and handled according to a priority structure that guarantees lower priority events will not be starved. Highest priority is usually given to memory fault recovery IO events. So if it happens that the disk drive has just recovered a segment requested by memory management at the same time your socket connection event happens, that data transfer to memory is going to be handled first while the socket IO event is queued. Fifteen seconds seems a rather long time, but not out of bounds. Could be your listener program is swapped out of memory in the interim.

IBMi is not a real-time system. If you need real-time, configure a dedicated Linux box to monitor and let it write to disk files on IBMi if needed, but be aware those writes will be queued, too. I'm currently enamored of using Raspberry PI for such tasks. $35.00 and free software. Linux is not purely "real-time" either, but you can configure a simple machine with very little else to get in the way of a fairly deterministic response.

The hardware guys on this forum might be able to help you configure an IBMi structured to be more responsive to your particular needs. Maybe they'll comment.

It appears from your email address (..@ProRaceTiming.com) that you're involved with timing races. I participate often in timed events and would hate to give up 15 seconds because a machine didn't respond. In fact, I'd be really pissed off. I expect my marathon time to be to the nearest hundredth of a second. Just because of this hobby, I've studied real-time machines a bit. IBMi is not the right hardware. Far better to get a time from the time clock before and put that time in the IP packet to the IBMi rather than relying on IBMi's response to an IP packet received event for time. Using the IBMi for recording the time created by the clock eliminates the need for reliance on immediate event handling.

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-
bounces@xxxxxxxxxxxx] On Behalf Of Rich Marion
Sent: Monday, August 05, 2013 10:18 PM
To: 'Midrange Systems Technical Discussion'
Subject: Socket Listener Delay Issue

All,

I have encountered a little intermittent problem with a program that is
monitoring a port for any incoming connections. It appears that it does
not get notified in a timely manner, sometimes, when there is a connection
request.

I set up a listen socket descriptor, then bind to the port, then set listen
with a parm of 100.

I have it log to a file the timestamp when a connection is received. I
accept the connection to an accept socket descriptor, and then spawn off
another job passing the accepted descriptor to the new job. Each incoming
request has its own spawned job to handle the communications. The
subsystem and jobqs are set to *NoMax.

My listener program logs every step to a log file with the time stamp it
happens.

Periodically, a network trace of the traffic will show the communications
between the remote device and the 400 NIC, but the program will not know
of
its existence until after a delay. Most of the time it processes the
request within a few micro seconds from when the remote device initiates
the
connection. But every so often, the 400 NIC will not inform my listener
program of the incoming transmission for up to 15 seconds.

I know for a fact the delay is between the 400 NIC and my listener program.
Network traces and my log files have proved this beyond any doubt. During
that delay, my listener program does continue accept and process other
requests. It has plenty of "Spare" time to handle the delayed request.

When it decides to have a delay, it affects multiple incoming requests.
(Each request is from a separate device.) We are at V7. Can anyone point me
in a direction to go or to a forum?

Thanks
Rich M.