[Bug 1884514] Comment bridged from LTC Bugzilla

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------- Comment From heinz-werner_seeck at de.ibm.com 2020-10-01 05:08 EDT-------
This functionallity will only be exploited on z15. On older HW it will be changed to the software implementation.

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Title:
  [FFe][20.10 FEAT] zlib/gzip hardware compression enablement

Status in Ubuntu on IBM z Systems:
  Triaged
Status in gzip package in Ubuntu:
  New
Status in zlib package in Ubuntu:
  New

Bug description:
  [Feature Freeze Exception]

  1. Feature:

  The latest s390x hardware comes with a new concept for hardware
  assisted compression/decompression, based on a 'Next Accelerator
  Function unit' (NXU). This is an on-chip concept, a co-processor for
  compression available to all cores on the same chip. It provides
  functions as normal 'problem state' instructions (in other words user
  space instructions that are directly consumable by libraries and
  applications) and supports DEFLATE compliant compression/decompression
  + GZIP CRC/ZLIB Adler.

  To enable this hardware support for zlib and gzip, zlib needs to be compiled with CFLAGS="-O2 -DDFLTCC -DDFLTCC_LEVEL_MASK=0x7e".
  The value of 0x7e enables hardware compression for the compression levels 1-6 (out of 0-9).
  There is a significant business value of having the enablement active by default, since tests on a system with 4 IFLs and hardware compression enabled this way offered (especially for DEFLATE as best case) a speed up of more than 40x.

  2. Changes

  Adding CFLAGS="-O2 -DDFLTCC -DDFLTCC_LEVEL_MASK=0x7e" attributes/macro
  during build of zlib and gzip.

  3. Regression risk

  The concept is new and comes with IBM z15 and LinuxONE III only and is with that specific and limited to s390x.
  Hence a potential regressions of this late addition would be limited to s390x and there again with the above changes to zlib (and gzip).
  In case of unforeseen issues with the NXU hardware component, a fallback to software is done.
  On top a modified zlib package was build and made available in a PPA for further testing.
  This change should have been included earlier, but was blocked by other zlib tickets/bugs that needed to be fixed and integrated first (like LP 1893170), hence this request for late addition.
  __________

  HW Compression need to be enabled with Default-Compression-Level 6.

  Adding following CFLAGS attributes during build of zlib and gzip
  "-DDFLTCC_LEVEL_MASK=0x7e"

  CFLAGS="-O2 -DDFLTCC -DDFLTCC_LEVEL_MASK=0x7e" ./configure

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