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Performance Improvements

The following items improve performance:

  • Fast CCW Translation for Network I/O
  • Enhanced Guest Page Fault Handling
  • CMSINST Shared Segment Addition

Fast CCW Translation for Network I/O

To improve the performance of guest I/O to network devices, the fast CCW translator in CP, previously limited to DASD channel programs, has been extended to handle a wide range of channel programs that perform I/Os to network adapters such as channel-to-channel adapters (CTCA), CLAW, OSA, and LAN Channel Station (LCS) devices. Although the fast CCW translation extensions are based on analysis of Linux guest channel programs, any VM guest that does qualifying I/Os will benefit.

This change improves performance by reducing the processor time required by CP to do guest I/O translation. Measurement results for a Linux guest show a 39% decrease in CP CPU time for I/O to an LCS adapter and a 44% decrease in CP CPU time for I/O to a real CTC adapter. See Fast CCW Translation for Network I/O for measurement details.

Enhanced Guest Page Fault Handling

Page fault handling support within CP has been enhanced to allow 31-bit or 64-bit guests to take full advantage of page fault notifications, allowing the guest to continue processing while the page fault is handled by CP. This support will be provided by APAR VM62840, which also makes it available on z/VM 3.1.0.

This support extends the current PFAULT page fault handshaking service in the following ways:

  • the guest does not have to be in access-register mode
  • z/Architecture is supported (includes 64-bit addressing)
  • the guest can use the PSW to mask off interrupts when not wanted

CMSINST Shared Segment Addition

DMSWRS MODULE has been added to the CMSINST shared segment, eliminating loading time and reducing real storage requirements for CMS environments that use SENDFILE.

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