Intel AS/400 RISC Server, 170 Servers, 7xx Servers manual 100

grows at a rate which can eventually eliminate server/batch capacity and limit additional interactive growth. It is best for interactive workloads to execute below (less than) the knee of the curve. (However, for those models having the knee at 1/3 of the total interactive capacity, satisfactory performance can be achieved.) The following graph illustrates these points.

Model 7xx and 9/98 Model 170 CPU CPU Distribution vs. Interactive Utilization

	100			Announced
				Capacities
%	80			Stop Here!
CPU	60	Available for		available
Available		Client/Server	Knee	overhead
	40
				interactive
	20
	0
	0		Full	7/6
		Fraction of Interactive CPW

Applies to: Model 170 announced in 9/98 and ALL systems announced on or after 2/99

Figure 2.1. Server Model behavior

The figure above shows a straight line for the effective interactive utilization. Real/customer environments will produce a curved line since most environments will be dynamic, due to job initiation, interrupts, etc.

In general, a single interactive job will not cause a significant impact to client/server performance

Microcode task CFINTn, for all iSeries models, handles interrupts, task switching, and other similar system overhead functions. For the server models, when interactive processing exceeds a threshold amount, the additional overhead required will be manifest in the CFINTn task. Note that a single interactive job will not incur this overhead.

There is one CFINTn task for each processor. For example, on a single processor system only CFINT1 will appear. On an 8-way processor, system tasks CFINT1 through CFINT8 will appear. It is possible to see significant CFINT activity even when server/interactive overhead does not exist. For example if there are lots of synchronous or communication I/O or many jobs with many task switches.

The effective interactive utilization (EIU) for a server system can be defined as the useable interactive utilization plus the total of CFINT utilization.

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 2 - Server Performance Behavior	19