[PATCH 0/5] S390 hardware compression support for kernel zlib

Mikhail Zaslonko
2019-11-26T14:41:50Z

With IBM z15 mainframe the new DFLTCC instruction is available. It
implements deflate algorithm in hardware (Nest Acceleration Unit - NXU)
with estimated compression and decompression performance orders of
magnitude faster than the current zlib.

This patch-set adds s390 hardware compression support to kernel zlib.
The code is based on the userspace zlib implementation:
https://github.com/madler/zlib/pull/410
The coding style is also preserved for future maintainability.
There is only limited set of userspace zlib functions represented in
kernel. Apart from that, all the memory allocation should be performed
in advance. Thus, the workarea structures are extended with the parameter
lists required for the DEFLATE CONVENTION CALL instruction.
Since kernel zlib itself does not support gzip headers, only Adler-32
checksum is processed (also can be produced by DFLTCC facility).
Like it was implemented for userspace, kernel zlib will compress in
hardware on level 1, and in software on all other levels. Decompression
will always happen in hardware (when enabled).
Two DFLTCC compression calls produce the same results only when they
both are made on machines of the same generation, and when the
respective buffers have the same offset relative to the start of the
page. Therefore care should be taken when using hardware compression
when reproducible results are desired. However it does always produce
the standard conform output which can be inflated anyway.
The new kernel command line parameter 'dfltcc' is introduced to
configure s390 zlib hardware support:
Format: { on | off | def_only | inf_only | always }
on: s390 zlib hardware support for compression on
level 1 and decompression (default)
off: No s390 zlib hardware support
def_only: s390 zlib hardware support for deflate
only (compression on level 1)
inf_only: s390 zlib hardware support for inflate
only (decompression)
always: Same as 'on' but ignores the selected compression
level always using hardware support (used for debugging)

The main purpose of the integration of the NXU support into the kernel zlib
is the use of hardware deflate in btrfs filesystem with on-the-fly
compression enabled. Apart from that, hardware support can also be used
during boot for decompressing the kernel or the ramdisk image

With the patch for btrfs expanding zlib buffer from 1 to 4 pages (patch 5)
the following performance results have been achieved using the ramdisk
with btrfs. These are relative numbers based on throughput rate and
compression ratio for zlib level 1:

Input data Deflate rate Inflate rate Compression ratio
NXU/Software NXU/Software NXU/Software
stream of zeroes 1.46 1.02 1.00
random ASCII data 10.44 3.00 0.96
ASCII text (dickens) 6,21 3.33 0.94
binary data (vmlinux) 8,37 3.90 1.02

This means that s390 hardware deflate can provide up to 10 times faster
compression (on level 1) and up to 4 times faster decompression (refers to
all compression levels) for btrfs zlib.

Disclaimer: Performance results are based on IBM internal tests using DD
command-line utility on btrfs on a Fedora 30 based internal driver in native
LPAR on a z15 system. Results may vary based on individual workload,
configuration and software levels.

Mikhail Zaslonko (5):
lib/zlib: Add s390 hardware support for kernel zlib_deflate
s390/boot: Rename HEAP_SIZE due to name collision
lib/zlib: Add s390 hardware support for kernel zlib_inflate
s390/boot: Add dfltcc= kernel command line parameter
btrfs: Increase buffer size for zlib functions

.../admin-guide/kernel-parameters.txt | 12 +
arch/s390/boot/compressed/decompressor.c | 8 +-
arch/s390/boot/ipl_parm.c | 14 +
arch/s390/include/asm/setup.h | 7 +
arch/s390/kernel/setup.c | 1 +
fs/btrfs/compression.c | 2 +-
fs/btrfs/zlib.c | 109 ++++---
lib/Kconfig | 22 ++
lib/Makefile | 1 +
lib/decompress_inflate.c | 13 +
lib/zlib_deflate/deflate.c | 79 ++---
lib/zlib_deflate/deftree.c | 54 ----
lib/zlib_deflate/defutil.h | 134 ++++++++-
lib/zlib_dfltcc/Makefile | 11 +
lib/zlib_dfltcc/dfltcc.c | 55 ++++
lib/zlib_dfltcc/dfltcc.h | 144 +++++++++
lib/zlib_dfltcc/dfltcc_deflate.c | 280 ++++++++++++++++++
lib/zlib_dfltcc/dfltcc_inflate.c | 149 ++++++++++
lib/zlib_dfltcc/dfltcc_syms.c | 17 ++
lib/zlib_dfltcc/dfltcc_util.h | 124 ++++++++
lib/zlib_inflate/inflate.c | 32 +-
lib/zlib_inflate/inflate.h | 8 +
lib/zlib_inflate/infutil.h | 18 +-
23 files changed, 1137 insertions(+), 157 deletions(-)
create mode 100644 lib/zlib_dfltcc/Makefile
create mode 100644 lib/zlib_dfltcc/dfltcc.c
create mode 100644 lib/zlib_dfltcc/dfltcc.h
create mode 100644 lib/zlib_dfltcc/dfltcc_deflate.c
create mode 100644 lib/zlib_dfltcc/dfltcc_inflate.c
create mode 100644 lib/zlib_dfltcc/dfltcc_syms.c
create mode 100644 lib/zlib_dfltcc/dfltcc_util.h

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2.17.1