commit 94b0dc9419bd038cb85b364a7556569386c31741
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Wed Jun 15 10:41:29 2022 -0700
x86: Add bounds `x86_non_temporal_threshold`
The lower-bound (16448) and upper-bound (SIZE_MAX / 16) are assumed
by memmove-vec-unaligned-erms.
The lower-bound is needed because memmove-vec-unaligned-erms unrolls
the loop aggressively in the L(large_memset_4x) case.
The upper-bound is needed because memmove-vec-unaligned-erms
right-shifts the value of `x86_non_temporal_threshold` by
LOG_4X_MEMCPY_THRESH (4) which without a bound may overflow.
The lack of lower-bound can be a correctness issue. The lack of
upper-bound cannot.
(cherry picked from commit b446822b6ae4e8149902a78cdd4a886634ad6321)
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 28ff502990c2a10f..5ab3212f34e3dc37 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -47,7 +47,7 @@ glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
glibc.elision.skip_lock_busy: 3 (min: -2147483648, max: 2147483647)
glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
-glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x4040, max: 0x0fffffffffffffff)
glibc.cpu.x86_shstk:
glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
index 560bf260e8fbd7bf..8f85f70858413ebe 100644
--- a/sysdeps/x86/dl-cacheinfo.h
+++ b/sysdeps/x86/dl-cacheinfo.h
@@ -931,8 +931,14 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
TUNABLE_SET_WITH_BOUNDS (x86_data_cache_size, data, 0, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_shared_cache_size, shared, 0, SIZE_MAX);
+ /* SIZE_MAX >> 4 because memmove-vec-unaligned-erms right-shifts the value of
+ 'x86_non_temporal_threshold' by `LOG_4X_MEMCPY_THRESH` (4) and it is best
+ if that operation cannot overflow. Minimum of 0x4040 (16448) because the
+ L(large_memset_4x) loops need 64-byte to cache align and enough space for
+ at least 1 iteration of 4x PAGE_SIZE unrolled loop. Both values are
+ reflected in the manual. */
TUNABLE_SET_WITH_BOUNDS (x86_non_temporal_threshold, non_temporal_threshold,
- 0, SIZE_MAX);
+ 0x4040, SIZE_MAX >> 4);
TUNABLE_SET_WITH_BOUNDS (x86_rep_movsb_threshold, rep_movsb_threshold,
minimum_rep_movsb_threshold, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_rep_stosb_threshold, rep_stosb_threshold, 1,