[PATCH v8 6/6] loongarch: Enable THP-aligned load segments by default on 64-bit

[H.J. Lu]

On Sun, Apr 5, 2026 at 11:56 AM WANG Rui <wangrui@loongson.cn> wrote:
>
> On LoongArch64 Linux, aligning ELF load segments to Transparent Huge Page
> (THP) boundaries provides consistent performance benefits for large
> binaries by reducing TLB pressure and improving instruction fetch
> efficiency.
>
> Enable THP-based load segment alignment by default on LoongArch64 by
> setting `glibc.elf.thp=1` during startup. Define the default THP
> page size for load segment alignment on LoongArch64 as 32MB.
>
> This allows the dynamic loader to apply THP-friendly alignment without
> requiring the `glibc.elf.thp` tunable to be explicitly set.
>
> Benchmarks
>
> Machine: Loongson 3A6000 (LoongArch64)
> Kernel: 6.18.13
>   CONFIG_READ_ONLY_THP_FOR_FS=y
>   CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
>
> Workload 1: building Cargo 1.93.0
> Rustc: nightly-2026-02-26
>
>                 Without patch        With patch
> instructions    3,690,358,948,176    3,690,301,774,568
> cpu-cycles      4,233,025,766,760    4,035,866,635,741
> itlb-misses     9,708,829,532        2,700,014,717
> time elapsed    302.40 s             289.68 s
>
> Instructions remain essentially unchanged. iTLB misses drop by about
> 72%, reducing CPU cycles by about 4.7% and wall time by about 4.2%.
>
> Workload 2: building Linux kernel v7.0-rc1
> LLVM: 21.1.8
>
>                 Without patch        With patch
> instructions    14,163,739,876,387   14,169,418,598,675
> cpu-cycles      19,231,890,317,741   16,851,494,928,181
> itlb-misses     91,142,010,440       90,779,245
> time elapsed    1022.09 s            893.22 s
>
> Instructions remain roughly the same. iTLB misses drop from about 91B
> to about 90M (roughly 99.9% reduction), reducing CPU cycles by about
> 12% and wall time by about 12.6%.
>
> Reviewed-by: caiyinyu <caiyinyu@loongson.cn>
> Signed-off-by: WANG Rui <wangrui@loongson.cn>
> ---
>  .../unix/sysv/linux/loongarch/cpu-features.c  |  6 +++++
>  .../loongarch/lp64/dl-map-segment-align.h     | 22 +++++++++++++++++++
>  2 files changed, 28 insertions(+)
>  create mode 100644 sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
>
> diff --git a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
> index 0c125e64e2b..7ed54ff53e7 100644
> --- a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
> +++ b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
> @@ -27,4 +27,10 @@ init_cpu_features (struct cpu_features *cpu_features)
>    GLRO(dl_larch_cpu_features).hwcap = GLRO(dl_hwcap);
>    TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *,
>                TUNABLE_CALLBACK (set_hwcaps));
> +
> +#ifdef __LP64__
> +  /* Enable THP-based load segment alignment by default on LoongArch64. */
> +  if (!TUNABLE_IS_INITIALIZED (glibc, elf, thp))
> +    TUNABLE_SET (glibc, elf, thp, 1);
> +#endif
>  }
> diff --git a/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h b/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
> new file mode 100644
> index 00000000000..c51ee4ac47e
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/loongarch/lp64/dl-map-segment-align.h
> @@ -0,0 +1,22 @@
> +/* _dl_map_segment_align.  LoongArch64 Linux version.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   Copyright The GNU Toolchain Authors.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#define DL_MAP_DEFAULT_THP_PAGESIZE (32 * 1024 * 1024)
>

What happens if DL_MAP_DEFAULT_THP_PAGESIZE is different
from /sys/kernel/mm/transparent_hugepage/hpage_pmd_size?

> +#include_next <dl-map-segment-align.h>
> --
> 2.53.0
>


-- 
H.J.