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After the update to zstd-1.4.10 passing -O3 is no longer necessary to get good performance from zstd. Using the default optimization level -O2 is sufficient to get good performance. I've measured no significant change to compression speed, and a ~1% decompression speed loss, which is acceptable. This fixes the reported parisc -Wframe-larger-than=1536 errors [0]. The gcc-8-hppa-linux-gnu compiler performed very poorly with -O3, generating stacks that are ~3KB. With -O2 these same functions generate stacks in the < 100B, completely fixing the problem. Function size deltas are listed below: ZSTD_compressBlock_fast_extDict_generic: 3800 -> 68 ZSTD_compressBlock_fast: 2216 -> 40 ZSTD_compressBlock_fast_dictMatchState: 1848 -> 64 ZSTD_compressBlock_doubleFast_extDict_generic: 3744 -> 76 ZSTD_fillDoubleHashTable: 3252 -> 0 ZSTD_compressBlock_doubleFast: 5856 -> 36 ZSTD_compressBlock_doubleFast_dictMatchState: 5380 -> 84 ZSTD_copmressBlock_lazy2: 2420 -> 72 Additionally, this improves the reported code bloat [1]. With gcc-11 bloat-o-meter shows an 80KB code size improvement: ``` > ../scripts/bloat-o-meter vmlinux.old vmlinux add/remove: 31/8 grow/shrink: 24/155 up/down: 25734/-107924 (-82190) Total: Before=6418562, After=6336372, chg -1.28% ``` Compared to before the zstd-1.4.10 update we see a total code size regression of 105KB, down from 374KB at v5.16-rc1: ``` > ../scripts/bloat-o-meter vmlinux.old vmlinux add/remove: 292/62 grow/shrink: 56/88 up/down: 235009/-127487 (107522) Total: Before=6228850, After=6336372, chg +1.73% ``` [0] https://lkml.org/lkml/2021/11/15/710 [1] https://lkml.org/lkml/2021/11/14/189 Link: https://lore.kernel.org/r/20211117014949.1169186-4-nickrterrell@gmail.com/ Link: https://lore.kernel.org/r/20211117201459.1194876-4-nickrterrell@gmail.com/ Reported-by: Geert Uytterhoeven <geert@linux-m68k.org> Tested-by: Geert Uytterhoeven <geert@linux-m68k.org> Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Nick Terrell <terrelln@fb.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.