diff options
| -rw-r--r-- | sysdeps/x86/dl-cacheinfo.h | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h index 43be2c1229..cd4d0351ae 100644 --- a/sysdeps/x86/dl-cacheinfo.h +++ b/sysdeps/x86/dl-cacheinfo.h @@ -745,8 +745,8 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) /* The default setting for the non_temporal threshold is [1/8, 1/2] of size of the chip's cache (depending on `cachesize_non_temporal_divisor` which - is microarch specific. The default is 1/4). For most Intel and AMD - processors with an initial release date between 2017 and 2023, a thread's + is microarch specific. The default is 1/4). For most Intel processors + with an initial release date between 2017 and 2023, a thread's typical share of the cache is from 18-64MB. Using a reasonable size fraction of L3 is meant to estimate the point where non-temporal stores begin out-competing REP MOVSB. As well the point where the fact that @@ -757,12 +757,21 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) the maximum thrashing capped at 1/associativity. */ unsigned long int non_temporal_threshold = shared / cachesize_non_temporal_divisor; + + /* If the computed non_temporal_threshold <= 3/4 * per-thread L3, we most + likely have incorrect/incomplete cache info in which case, default to + 3/4 * per-thread L3 to avoid regressions. */ + unsigned long int non_temporal_threshold_lowbound + = shared_per_thread * 3 / 4; + if (non_temporal_threshold < non_temporal_threshold_lowbound) + non_temporal_threshold = non_temporal_threshold_lowbound; + /* If no ERMS, we use the per-thread L3 chunking. Normal cacheable stores run a higher risk of actually thrashing the cache as they don't have a HW LRU hint. As well, their performance in highly parallel situations is noticeably worse. */ if (!CPU_FEATURE_USABLE_P (cpu_features, ERMS)) - non_temporal_threshold = shared_per_thread * 3 / 4; + non_temporal_threshold = non_temporal_threshold_lowbound; /* 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 |