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

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ef044cc6d79c5646b521569417da890154ea1813

commit ef044cc6d79c5646b521569417da890154ea1813
Author: WANG Rui <[email protected]>
Date:   Tue Apr 14 15:26:58 2026 +0000

    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 <[email protected]>
    Signed-off-by: WANG Rui <[email protected]>

Diff:
---
 sysdeps/unix/sysv/linux/loongarch/cpu-features.c   |  6 ++++++
 .../linux/loongarch/lp64/dl-map-segment-align.h    | 22 ++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/loongarch/cpu-features.c b/sysdeps/unix/sysv/linux/loongarch/cpu-features.c
index 0c125e64e2..7ed54ff53e 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 0000000000..c51ee4ac47
--- /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>