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18 S/390 PID: ThinkPad Enabled for S/390
You can emulate a S/390 with a number of CPUs. This number cannot exceed the
number of PC processors licensed for S/390 emulation. With the ThinkPad/EFS system
we are describing, this means that only a single-processor S/390 can be emulated.
The emulated S/390 can use LAN adapter(s) on the ThinkPad. OS/390 TCP/IP can run
this way. A single ThinkPad LAN adapter can be used both by the OS/390 TCP/IP and by
Linux TCP/IP. This differs from FLEX-ES under UnixWare, where a LAN adapter may not
be shared by a S/390 TCP/IP and UnixWare.
3
The FLEX-ES Terminal Solicitor is a Linux process. It provides a TN3270 server function
and listens (by default) on port 24 of Linux’s TCP/IP. An external user can connect a
TN3270 client to the Terminal Solicitor. The Terminal Solicitor and the FLEX-ES emulation
process will then transform the TN3270 protocol so that it appears to be a local, non-SNA
3270 to the emulated S/390. This is the normal way to connect MVS consoles, TSO
terminals, CICS terminals, and so forth. There is no particular limit to the number of
terminals that can be connected this way.
4
Each one must have appropriate VTAM
definitions for a local 3270, of course.
If a LAN adapter is connected to OS/390 TCP/IP, then TSO terminals may connect this
way. If OS/390 TCP/IP and UNIX System Services are configured for it, ASCII telnet
sessions can also use this connection. The Terminal Solicitor is not involved in these
connections. The two LAN interfaces would have separate IP addresses, of course, even
though they may share a common LAN adapter.
The illustration shows a single emulated S/390. It is possible to emulate several S/390s at
the same time.
5
The PC processor(s) licensed for S/390 emulation will be dispatched
among the several emulated S/390s. Only one Terminal Solicitor would be used; it can be
shared by all emulated S/390s. The multiple emulated S/390s are known as multiple
instances of FLEX-ES S/390 emulation. Multiple S/390 instances of OS/390 are probably
not very practical with a ThinkPad/EFS system, due to limited ThinkPad memory and due
to there being a single ThinkPad processor that must be shared among all the S/390
instances plus Linux. However, multiple VSE/ESA or VM/ESA systems might be practical
on a ThinkPad/EFS machine.
While it is not apparent in the illustration, the amount of real PC memory available is a key
performance factor. The performance of an emulated S/390 degrades quickly if Linux
performs much paging (especially if the paging is triggered by FLEX-ES processes or if
the memory being paged is used by FLEX-ES to emulate S/390 real memory). The
recommended paging level for Linux is zero once steady-state S/390 emulation is running,
and should seldom rise to more than one page per second. OS/390 paging (in the
emulated S/390) might be much higher than this, with no ill effects. Do not confuse Linux
paging with OS/390 paging. The amount of real ThinkPad memory available is a key factor
in setting the size of the emulated S/390 machine memory and in deciding whether to use
multiple S/390 instances.
The terminal shown in the figure is usually the ThinkPad display and keyboard. The
typical ThinkPad/EFS usage would be through X Windows. In this mode, several windows
can be open. Some of these might be x3270 sessions (TN3270 clients) connected to
OS/390 through the Terminal Solicitor; one of these sessions might be the MVS master
console. Another window might have FLEX-ES command line interface (CLI) prompts
used to control FLEX-ES operation. CLI commands are used to IPL a S/390 operating
system, for example.
3
It also differs from P/390-based machines and the MP3000, none of which permit sharing of LAN adapters by
multiple TCP/IP stacks.
4
There is an overall FLEX-ES limitation of 2048 emulated devices, but a ThinkPad/EFS system is unlikely to
approach this limit.
5
A different FLEX-ES license is not required for this. The FLEX-ES license indicates how many Server processors
may be used for S/390 operation, but does not limit how many instances of S/390s you can run.