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| author | Noah Goldstein <goldstein.w.n@gmail.com> | 2022-06-15 10:41:29 -0700 |
|---|---|---|
| committer | Noah Goldstein <goldstein.w.n@gmail.com> | 2022-06-15 14:25:55 -0700 |
| commit | b446822b6ae4e8149902a78cdd4a886634ad6321 (patch) | |
| tree | 417d3ee01f93bd92db817203660b6f8591f625f8 /sysdeps/x86 | |
| parent | 686216945a7873237bf892bbe38a2eef23aadeba (diff) | |
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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.
Diffstat (limited to 'sysdeps/x86')
| -rw-r--r-- | sysdeps/x86/dl-cacheinfo.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h index cc3b840f9c..e9f3382108 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, |