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[2603:8080:1301:76c6:d514:288c:2603:6ec7]) by smtp.gmail.com with ESMTPSA id mc27-20020a170906eb5b00b00966330021e9sm3141378ejb.47.2023.05.10.15.12.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 May 2023 15:12:36 -0700 (PDT) From: Noah Goldstein To: libc-alpha@sourceware.org Cc: goldstein.w.n@gmail.com, hjl.tools@gmail.com, carlos@systemhalted.org Subject: [PATCH v7 3/4] x86: Make the divisor in setting `non_temporal_threshold` cpu specific Date: Wed, 10 May 2023 17:12:12 -0500 Message-Id: <20230510221213.765754-2-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230510221213.765754-1-goldstein.w.n@gmail.com> References: <20230424050329.1501348-1-goldstein.w.n@gmail.com>v7-0001-x86-Increase-non_temporal_threshold-to-roughly-si.patch> <20230510221213.765754-1-goldstein.w.n@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-12.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Different systems prefer a different divisors. >From benchmarks[1] so far the following divisors have been found: ICX : 2 SKX : 2 BWD : 8 For Intel, we are generalizing that BWD and older prefers 8 as a divisor, and SKL and newer prefers 2. This number can be further tuned as benchmarks are run. [1]: https://github.com/goldsteinn/memcpy-nt-benchmarks --- sysdeps/x86/cpu-features.c | 16 +++++++++++++-- sysdeps/x86/dl-cacheinfo.h | 32 ++++++++++++++++++------------ sysdeps/x86/include/cpu-features.h | 3 +++ 3 files changed, 36 insertions(+), 15 deletions(-) diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index 9d433f8144..4cc1cd9fed 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -637,6 +637,7 @@ init_cpu_features (struct cpu_features *cpu_features) unsigned int stepping = 0; enum cpu_features_kind kind; + cpu_features->cachesize_non_temporal_divisor = 4; #if !HAS_CPUID if (__get_cpuid_max (0, 0) == 0) { @@ -720,8 +721,8 @@ init_cpu_features (struct cpu_features *cpu_features) of Core i3/i5/i7 processors if AVX is available. */ if (!CPU_FEATURES_CPU_P (cpu_features, AVX)) break; - case INTEL_BIGCORE_NEHALEM: - case INTEL_BIGCORE_WESTMERE: + + enable_modern_features: /* Rep string instructions, unaligned load, unaligned copy, and pminub are fast on Intel Core i3, i5 and i7. */ cpu_features->preferred[index_arch_Fast_Rep_String] @@ -730,11 +731,20 @@ init_cpu_features (struct cpu_features *cpu_features) | bit_arch_Prefer_PMINUB_for_stringop); break; + case INTEL_BIGCORE_NEHALEM: + case INTEL_BIGCORE_WESTMERE: + /* Older CPUs prefer non-temporal stores at lower threshold. */ + cpu_features->cachesize_non_temporal_divisor = 8; + goto enable_modern_features; + /* Default tuned Bigcore microarch. */ case INTEL_BIGCORE_SANDYBRIDGE: case INTEL_BIGCORE_IVYBRIDGE: case INTEL_BIGCORE_HASWELL: case INTEL_BIGCORE_BROADWELL: + cpu_features->cachesize_non_temporal_divisor = 8; + goto default_tuning; + case INTEL_BIGCORE_SKYLAKE: case INTEL_BIGCORE_AMBERLAKE: case INTEL_BIGCORE_COFFEELAKE: @@ -755,11 +765,13 @@ init_cpu_features (struct cpu_features *cpu_features) case INTEL_BIGCORE_SAPPHIRERAPIDS: case INTEL_BIGCORE_EMERALDRAPIDS: case INTEL_BIGCORE_GRANITERAPIDS: + cpu_features->cachesize_non_temporal_divisor = 2; goto default_tuning; /* Default tuned Mixed (bigcore + atom SOC). */ case INTEL_MIXED_LAKEFIELD: case INTEL_MIXED_ALDERLAKE: + cpu_features->cachesize_non_temporal_divisor = 2; goto default_tuning; } diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h index 4a1a5423ff..864b00a521 100644 --- a/sysdeps/x86/dl-cacheinfo.h +++ b/sysdeps/x86/dl-cacheinfo.h @@ -738,19 +738,25 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) cpu_features->level3_cache_linesize = level3_cache_linesize; cpu_features->level4_cache_size = level4_cache_size; - /* The default setting for the non_temporal threshold is 1/4 of size - of the chip's cache. For most Intel and AMD processors with an - initial release date between 2017 and 2023, a thread's typical - share of the cache is from 18-64MB. Using the 1/4 L3 is meant to - estimate the point where non-temporal stores begin outcompeting - REP MOVSB. As well the point where the fact that non-temporal - stores are forced back to main memory would already occurred to the - majority of the lines in the copy. Note, concerns about the - entire L3 cache being evicted by the copy are mostly alleviated - by the fact that modern HW detects streaming patterns and - provides proper LRU hints so that the maximum thrashing - capped at 1/associativity. */ - unsigned long int non_temporal_threshold = shared / 4; + unsigned long int cachesize_non_temporal_divisor + = cpu_features->cachesize_non_temporal_divisor; + if (cachesize_non_temporal_divisor <= 0) + cachesize_non_temporal_divisor = 4; + + /* The default setting for the non_temporal threshold is [1/2, 1/8] of size + of the chip's cache (depending on `cachesize_non_temporal_divisor` which + is microarch specific. The defeault is 1/4). For most Intel and AMD + 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 outcompeting REP MOVSB. As well the point where the fact that + non-temporal stores are forced back to main memory would already occurred + to the majority of the lines in the copy. Note, concerns about the entire + L3 cache being evicted by the copy are mostly alleviated by the fact that + modern HW detects streaming patterns and provides proper LRU hints so that + the maximum thrashing capped at 1/associativity. */ + unsigned long int non_temporal_threshold + = shared / cachesize_non_temporal_divisor; /* 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, there performance in highly parallel situations is diff --git a/sysdeps/x86/include/cpu-features.h b/sysdeps/x86/include/cpu-features.h index 40b8129d6a..f5b9dd54fe 100644 --- a/sysdeps/x86/include/cpu-features.h +++ b/sysdeps/x86/include/cpu-features.h @@ -915,6 +915,9 @@ struct cpu_features unsigned long int shared_cache_size; /* Threshold to use non temporal store. */ unsigned long int non_temporal_threshold; + /* When no user non_temporal_threshold is specified. We default to + cachesize / cachesize_non_temporal_divisor. */ + unsigned long int cachesize_non_temporal_divisor; /* Threshold to use "rep movsb". */ unsigned long int rep_movsb_threshold; /* Threshold to stop using "rep movsb". */ -- 2.34.1