From ed2f9dc9420c4c61436328778a70459d0a35556a Mon Sep 17 00:00:00 2001 From: Noah Goldstein Date: Mon, 8 May 2023 22:10:20 -0500 Subject: [PATCH] x86: Use 64MB as nt-store threshold if no cacheinfo [BZ #30429] Content-type: text/plain; charset=UTF-8 If `non_temporal_threshold` is below `minimum_non_temporal_threshold`, it almost certainly means we failed to read the systems cache info. In this case, rather than defaulting the minimum correct value, we should default to a value that gets at least reasonable performance. 64MB is chosen conservatively to be at the very high end. This should never cause non-temporal stores when, if we had read cache info, we wouldn't have otherwise. Reviewed-by: Florian Weimer --- sysdeps/x86/dl-cacheinfo.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h index ec88945b39..877e73d700 100644 --- a/sysdeps/x86/dl-cacheinfo.h +++ b/sysdeps/x86/dl-cacheinfo.h @@ -749,8 +749,16 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) reflected in the manual. */ unsigned long int maximum_non_temporal_threshold = SIZE_MAX >> 4; unsigned long int minimum_non_temporal_threshold = 0x4040; + + /* If `non_temporal_threshold` less than `minimum_non_temporal_threshold` + it most likely means we failed to detect the cache info. We don't want + to default to `minimum_non_temporal_threshold` as such a small value, + while correct, has bad performance. We default to 64MB as reasonable + default bound. 64MB is likely conservative in that most/all systems would + choose a lower value so it should never forcing non-temporal stores when + they otherwise wouldn't be used. */ if (non_temporal_threshold < minimum_non_temporal_threshold) - non_temporal_threshold = minimum_non_temporal_threshold; + non_temporal_threshold = 64 * 1024 * 1024; else if (non_temporal_threshold > maximum_non_temporal_threshold) non_temporal_threshold = maximum_non_temporal_threshold; -- 2.39.3