VM/370 EXTENDED CONTROL-PROGRAM SUPPORT (ECPS) VM/370 Extended Control-Program Support (ECPS) improves the performance
of the processor when executing V!/370 beyond the improvement attained by the virtual machine assist feature described above. See V!/370 flanni~g and System Ge~tion Guide for a list of the processors on
which ECPS is available. ECPS consists of three parts: CP assist,
expanded virtual machine assist, and virtual interval timer assist. I detailed description of ECPS is provided in "Appendix I. V!/370 Extended Control-program Support." £f Assist
The CP assist part of ECPS assists various routines that are frequently used by V!/370. Because these routines are assisted by the hardware without involving V!/310. performance of the V!/370 system is improved.
The high-use paths of the following functions are assisted: • Get Free Space (D!KFRE) • Release Free Space (DKKFRE) • Untranslate CSI (DMKUNT) • Free CCI Storage (D!KUNT) • Locate' irtual I/O Control Block (DKKSCI) • Locate Real I/O Control Block (D!KSCN) • Lock a page (D!KPTR) • Unlock a page (D!KPTR) • Common CCW co.mand processing (D!KCCW) • Decode First CCI co •• and (D!KCCW) • Decode following CCW command (D!KCCW) • TRANBRNG subroutine (D!KCCW) • TRANLOCK subroutine (D!KCCW) • Invalidate page table subroutine (D!KV1T) • Invalidate segment table subroutine (D!KVl T) • !ai.n entry to dispatch (D!KDSP) • Dispatch a block or virtual machine (D!KDSP) • svc 8 (LINK) • SVC 12 (RETURN) • Locate changed shared pages (D!KV!l) Expanded virtual machine assist extends the level of handling of the
following privileged instructions: • LPSW • STNS! • STOS! • 55! In addition, expanded virtual machine assist handles
of the following privileged instructions not handled machine assist feature: • PTLB • SIO • SPT • SCKC • STPT • TCH the processing by the virtual
CP Introduction 1-37

Virtual interval timer assist provides hardware updating of the virtual
interval timer at virtual location 1'50'. This results in an update frequency of approximately 300 times per second, the same as for the
real interval timer. Procedures that use the virtual interval timer for
job accounting, performance measurements, and the like, will therefore
generate more accurate and repeatable time data than they would if the
virtual timer was being updated by CP routines. VM/370 Extended Control-program Support (ECPS) is controlled at two
levels: the VK/370 system and the virtual machine. At the i5i370 system level, ~~~b is automatically enabled when the system is loaded. The class A command:
set cpassist off
vi11 disable both CP assist and expanded virtual machine assist. The
class A command:
set sassist off
disables only the expanded virtual machine assist part of ECPS as ve11
as the virtual machine assist. CP assist is the only part of ECPS that
is truly independent.
At the virtual machine level, whenever ECPS is enabled on the system, both expanded virtual machine assist and virtual interval timer assist
are automatically enabled when you log on. If you issue the class G
command:
set assist off both assists as well as the existing virtual machine assist are
disabled. If you issue:
set assist notmr only the virtual interval timer assist is disabled. If CP assist is
disabled for the systea, the class A command: set sassist on
vi11 enable the virtual machine assist. You can then aachine assist and virtual interval timer assist for aachine by issuing the class A command: set assist on tar enable virtual
your virtual The restrictions on the use of ECPS are the same as those described for
the virtual machine assist feature vith one addition. Whenever a
virtual aachine traces external interrupts, the virtual interval timer 1-38 IBM VK/370 System Logic and Problem Determination--Vo1ume 1