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Message-Id: <20260113082748.250916-1-jiangfeng@kylinos.cn>
Date: Tue, 13 Jan 2026 16:27:34 +0800
From: Feng Jiang <jiangfeng@...inos.cn>
To: pjw@...nel.org,
palmer@...belt.com,
aou@...s.berkeley.edu,
alex@...ti.fr,
kees@...nel.org,
andy@...nel.org,
akpm@...ux-foundation.org,
jiangfeng@...inos.cn,
ebiggers@...nel.org,
martin.petersen@...cle.com,
ardb@...nel.org,
ajones@...tanamicro.com,
conor.dooley@...rochip.com,
samuel.holland@...ive.com,
linus.walleij@...aro.org,
nathan@...nel.org
Cc: linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: [PATCH v2 00/14] riscv: optimize string functions and add kunit tests
This series introduces optimized assembly implementations for strnlen,
strchr, and strrchr on the RISC-V architecture. To support a rigorous
verification process, the series also significantly expands the
string_kunit test suite with both functional correctness tests and
performance benchmarks.
The patchset is organized as follows:
- Refactoring (Patches 1-4): Extract generic C implementations for
strlen, strnlen, strchr, and strrchr into exported __generic_* functions.
- Correctness Testing (Patches 5-7): Extend string_kunit with detailed
functional tests for the target functions.
- Performance Benchmarking (Patches 8-11): Add a benchmarking framework
to string_kunit to measure execution time across various string lengths.
- RISC-V Optimizations (Patches 12-14): Provide the optimized assembly
implementations for the RISC-V architecture.
Testing:
All patches have been verified using the KUnit framework on QEMU
virt machine (riscv64). All string-related tests passed.
$ ./tools/testing/kunit/kunit.py run --arch=riscv \
--cross_compile=riscv64-linux-gnu- \
--kunitconfig=my_string.kunitconfig \
--raw_output
[15:26:26] Configuring KUnit Kernel ...
...
ok 1 string_test_memset16
ok 2 string_test_memset32
ok 3 string_test_memset64
ok 4 string_test_strlen
# string_test_strlen_bench: strlen performance (short, len: 8, iters: 100000):
# string_test_strlen_bench: arch-optimized: 148900 ns
# string_test_strlen_bench: generic C: 5551900 ns
# string_test_strlen_bench: speedup: 37.28x
# string_test_strlen_bench: strlen performance (medium, len: 64, iters: 100000):
# string_test_strlen_bench: arch-optimized: 166000 ns
# string_test_strlen_bench: generic C: 16250200 ns
# string_test_strlen_bench: speedup: 97.89x
# string_test_strlen_bench: strlen performance (long, len: 2048, iters: 10000):
# string_test_strlen_bench: arch-optimized: 14100 ns
# string_test_strlen_bench: generic C: 35605600 ns
# string_test_strlen_bench: speedup: 2525.21x
ok 5 string_test_strlen_bench
ok 6 string_test_strnlen
# string_test_strnlen_bench: strnlen performance (short, len: 8, iters: 100000):
# string_test_strnlen_bench: arch-optimized: 147500 ns
# string_test_strnlen_bench: generic C: 6429800 ns
# string_test_strnlen_bench: speedup: 43.59x
# string_test_strnlen_bench: strnlen performance (medium, len: 64, iters: 100000):
# string_test_strnlen_bench: arch-optimized: 197900 ns
# string_test_strnlen_bench: generic C: 22322500 ns
# string_test_strnlen_bench: speedup: 112.79x
# string_test_strnlen_bench: strnlen performance (long, len: 2048, iters: 10000):
# string_test_strnlen_bench: arch-optimized: 14100 ns
# string_test_strnlen_bench: generic C: 56162600 ns
# string_test_strnlen_bench: speedup: 3983.16x
ok 7 string_test_strnlen_bench
ok 8 string_test_strchr
# string_test_strchr_bench: strchr performance (short, len: 8, iters: 100000):
# string_test_strchr_bench: arch-optimized: 166800 ns
# string_test_strchr_bench: generic C: 6079400 ns
# string_test_strchr_bench: speedup: 36.44x
# string_test_strchr_bench: strchr performance (medium, len: 64, iters: 100000):
# string_test_strchr_bench: arch-optimized: 151500 ns
# string_test_strchr_bench: generic C: 21130400 ns
# string_test_strchr_bench: speedup: 139.47x
# string_test_strchr_bench: strchr performance (long, len: 2048, iters: 10000):
# string_test_strchr_bench: arch-optimized: 32800 ns
# string_test_strchr_bench: generic C: 50630400 ns
# string_test_strchr_bench: speedup: 1543.60x
ok 9 string_test_strchr_bench
ok 10 string_test_strnchr
ok 11 string_test_strrchr
# string_test_strrchr_bench: strrchr performance (short, len: 8, iters: 100000):
# string_test_strrchr_bench: arch-optimized: 166300 ns
# string_test_strrchr_bench: generic C: 6201400 ns
# string_test_strrchr_bench: speedup: 37.29x
# string_test_strrchr_bench: strrchr performance (medium, len: 64, iters: 100000):
# string_test_strrchr_bench: arch-optimized: 207200 ns
# string_test_strrchr_bench: generic C: 23062700 ns
# string_test_strrchr_bench: speedup: 111.30x
# string_test_strrchr_bench: strrchr performance (long, len: 2048, iters: 10000):
# string_test_strrchr_bench: arch-optimized: 14000 ns
# string_test_strrchr_bench: generic C: 51192900 ns
# string_test_strrchr_bench: speedup: 3656.63x
ok 12 string_test_strrchr_bench
ok 13 string_test_strspn
...
# string: pass:28 fail:0 skip:0 total:28
# Totals: pass:28 fail:0 skip:0 total:28
ok 1 string
reboot: Restarting system
[15:28:10] Elapsed time: 103.449s total, 0.001s configuring, 101.878s building, 1.569s running
Changes:
v1: Initial submission.
v2:
- Refactored lib/string.c to export __generic_* functions and added
corresponding functional/performance tests for strnlen, strchr,
and strrchr (Andy Shevchenko).
- Replaced magic numbers with STRING_TEST_MAX_LEN etc. (Andy Shevchenko).
---
Feng Jiang (14):
lib/string: extract generic strlen() into __generic_strlen()
lib/string: extract generic strnlen() into __generic_strnlen()
lib/string: extract generic strchr() into __generic_strchr()
lib/string: extract generic strrchr() into __generic_strrchr()
lib/string_kunit: add correctness test for strlen
lib/string_kunit: add correctness test for strnlen
lib/string_kunit: add correctness test for strrchr()
lib/string_kunit: add performance benchmark for strlen()
lib/string_kunit: add performance benchmark for strnlen()
lib/string_kunit: add performance benchmark for strchr()
lib/string_kunit: add performance benchmark for strrchr()
riscv: lib: add strnlen implementation
riscv: lib: add strchr implementation
riscv: lib: add strrchr implementation
arch/riscv/include/asm/string.h | 9 +
arch/riscv/lib/Makefile | 3 +
arch/riscv/lib/strchr.S | 35 ++++
arch/riscv/lib/strnlen.S | 164 +++++++++++++++
arch/riscv/lib/strrchr.S | 37 ++++
arch/riscv/purgatory/Makefile | 11 +-
include/linux/string.h | 4 +
lib/string.c | 53 +++--
lib/tests/string_kunit.c | 344 ++++++++++++++++++++++++++++++++
9 files changed, 645 insertions(+), 15 deletions(-)
create mode 100644 arch/riscv/lib/strchr.S
create mode 100644 arch/riscv/lib/strnlen.S
create mode 100644 arch/riscv/lib/strrchr.S
--
2.25.1
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