linux-kernel - [GIT PULL] zstd fixes for v5.16-rc1

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Message-ID: <1F7E17E1-9B51-4D21-B7FB-9BD3BE4A199A@fb.com>
Date:   Thu, 18 Nov 2021 21:22:35 +0000
From:   Nick Terrell <terrelln@...com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>,
        Helge Deller <deller@....de>
Subject: [GIT PULL] zstd fixes for v5.16-rc1

Hi Linus,

The following changes since commit fa55b7dcdc43c1aa1ba12bca9d2dd4318c2a0dbf:

  Linux 5.16-rc1 (2021-11-14 13:56:52 -0800)

are available in the Git repository at:

  git://github.com/terrelln/linux.git tags/zstd-for-linus-5.16-rc1

for you to fetch changes up to 7416cdc9b9c10968c57b1f73be5d48b3ecdaf3c8:

  lib: zstd: Don't add -O3 to cflags (2021-11-18 13:16:22 -0800)

Best,
Nick Terrell

----------------------------------------------------------------
zstd fixes for v5.16-rc1

Fix stack usage on parisc & improve code size bloat

This PR contains 3 commits:

1. Fixes a minor unused variable warning reported by Kernel test robot [0].
2. Improves the reported code bloat (-88KB / 374KB) [1] by outlining
   some functions that are unlikely to be used in performance sensitive
   workloads.
3. Fixes the reported excess stack usage on parisc [2] by removing -O3
   from zstd's compilation flags. -O3 triggered bugs in the hppa-linux-gnu
   gcc-8 compiler. -O2 performance is acceptable: neutral compression,
   about -1% decompression speed. We also reduce code bloat
   (-105KB / 374KB).

After this commit our code bloat is cut from 374KB to 105KB with gcc-11.
If we wanted to cut the remaining 105KB we'd likely have to trade
signicant performance, so I want to say that this is enough for now.

We should be able to get further gains without sacrificing speed, but
that will take some significant optimization effort, and isn't suitable
for a quick fix. I've opened an upstream issue [3] to track the code size,
and try to avoid future regressions, and improve it in the long term.

[0] https://lore.kernel.org/linux-mm/202111120312.833wII4i-lkp@intel.com/T/
[1] https://lkml.org/lkml/2021/11/15/710
[2] https://lkml.org/lkml/2021/11/14/189
[3] https://github.com/facebook/zstd/issues/2867

Link: https://lore.kernel.org/r/20211117014949.1169186-1-nickrterrell@gmail.com/
Link: https://lore.kernel.org/r/20211117201459.1194876-1-nickrterrell@gmail.com/

Signed-off-by: Nick Terrell <terrelln@...com>

----------------------------------------------------------------
Nick Terrell (3):
      lib: zstd: Fix unused variable warning
      lib: zstd: Don't inline functions in zstd_opt.c
      lib: zstd: Don't add -O3 to cflags

 lib/zstd/Makefile                            |  2 --
 lib/zstd/common/compiler.h                   |  7 +++++++
 lib/zstd/compress/zstd_compress_superblock.c |  2 ++
 lib/zstd/compress/zstd_opt.c                 | 12 ++++++++++++
 4 files changed, 21 insertions(+), 2 deletions(-)