loongarch: Enable THP-aligned load segments by default on 64-bit

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>

diff --git a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
index 0c125e64e2bc16abb28f86f157f354e9f3c9c5df..7ed54ff53e762ccc78e676e5d8545fed51f93375 100644 (file)
--- 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 (file)
index 0000000..c51ee4a
--- /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)
+
+#include_next <dl-map-segment-align.h>