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Performance Improvements
The following items improve performance:
- Contiguous Frame Management Improvements
- Improved Management of Idle Guests with Pending Network I/O
- No Pageable CP Modules
The use of the 64-bit architecture by CP results in a greater demand
for data structures that require contiguous frames, particularly those
associated with dynamic address translation. This line item involves
various algorithmic changes to improve the management of contiguous
frames. These changes have the potential to improve system performance
and avoid potential system hangs when memory is constrained and/or
fragmented. While very few field problems have been identified in
existing releases, these improvements help ensure that systems will
continue to run well as memory usage increases.
A problem was found on previous VM releases where guests were not
being dropped from the dispatch list when they went idle. This was
because those guests had network I/O outstanding even though network
I/O is often long-term. Such guests appeared runnable with high I/O
active wait state percentages.
APAR VM63282
addresses this problem for fully simulated network devices.
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Guests that have outstanding
network I/O to such devices but are otherwise idle are now considered
to be idle. This causes applicable guests to be appropriately dropped
from the dispatch list, allowing their storage to be more effectively
identified as available for other purposes. It also causes their user
state sampling to shift from I/O active wait state to idle or test idle
state. This APAR has been integrated into z/VM 5.1.0. The integrated
version has been extended so that it also applies to real devices that
are attached to a virtual machine and that have the same device codes
as those supported by the APAR.
With z/VM 5.1.0, all CP modules now reside in fixed storage.
Measurement results indicate that this has resulted in a small net
performance improvement in most situations due to reduced module
linkage overhead. Years ago, when real storage sizes were much
smaller, the ability to make infrequently used CP modules pageable
provided a meaningful performance advantage but now storage sizes are
so large that this design is no longer necessary.
Footnotes:
- 1
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VM63282 is available for z/VM 4.3.0 (PTF UM30888) and z/VM 4.4.0
(PTF UM30889). It applies to virtual (simulated) devices with the
following properties:
VDEVCLAS=CLASSPEC VDEVTYPE=TYPOSA OSA2 / OSA-E QDIO / HiperSockets
VDEVCLAS=CLASSPEC VDEVTYPE=TYPFCP FCP subchannel
VDEVCLAS=CLASSPEC VDEVTYPE=TYPCTCA CTCA / 3088 / ESCON / FICON
VDEVCLAS=CLASSVCM VDEVTYPE=TYPMSGF Msg Facility device
Virtual devices are those created by CP DEFINE commands, SPECIAL
directory statements and NICDEF directory statements.
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