linux-kernel - [PATCH v2 0/3] Fix stack usage on parisc & improve code size bloat

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Message-Id: <20211117201459.1194876-1-nickrterrell@gmail.com>
Date:   Wed, 17 Nov 2021 12:14:56 -0800
From:   Nick Terrell <nickrterrell@...il.com>
To:     Nick Terrell <terrelln@...com>
Cc:     linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v2 0/3] Fix stack usage on parisc & improve code size bloat

From: Nick Terrell <terrelln@...com>

I'll be sending these patches to Linus through my tree. Just submitting them
for comment before I do so. I'm somewhat unsure of the correct workflow for
patches I submit myself, so let me know if there is something different I
should do.

This patch set 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

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

v1 -> v2:
* (1/3) Update commit message & add a comment.

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                 | 14 +++++++++++++-
 4 files changed, 22 insertions(+), 3 deletions(-)

--
2.33.1