From: vmakarov@... Date: 2016-11-02T16:45:06+00:00 Subject: [ruby-core:77865] [Ruby trunk Feature#12142] Hash tables with open addressing Issue #12142 has been updated by Vladimir Makarov. Koichi Sasada wrote: > Sorry for my lazy-ness, I evaluated your two implementations (ffalcon has two versions, HUGEHASH or not). > > Now, I depicted all of my evaluations in charts, so I introduce this report: > I'll add explanation of this evaluation soon. Koichi, thank you for your detail investigation of the two tables. Looking at this report, I got an impression that you spent more time on this report than we spent time on our implementations. For the record, here is my comparison the same tables on different tests (MRI hash table benchmarks) as a speed up ratio vs trunk: ``` Yura Yura64 My bighash 1.657 1.751 1.612 hash_aref_dsym 0.929 0.927 0.967 hash_aref_dsym_long 1.314 1.444 1.427 hash_aref_fix 0.981 0.974 1.051 hash_aref_flo 1.662 1.656 1.908 hash_aref_miss 1.213 1.195 1.209 hash_aref_str 1.217 1.250 1.338 hash_aref_sym 0.924 0.932 0.992 hash_aref_sym_long 1.001 1.003 1.042 hash_flatten 1.082 1.091 1.184 hash_ident_flo 0.912 0.919 0.970 hash_ident_num 0.924 0.918 0.971 hash_ident_obj 0.878 0.876 0.963 hash_ident_str 0.902 0.896 0.960 hash_ident_sym 0.952 0.950 0.978 hash_keys 2.730 2.806 2.813 hash_long 1.439 1.463 1.564 hash_shift 1.297 1.283 1.403 hash_shift_u16 1.229 1.325 1.387 hash_shift_u24 1.224 1.201 1.378 hash_shift_u32 1.220 1.201 1.376 hash_small2 1.081 0.985 1.040 hash_small4 1.055 0.980 1.050 hash_small8 2.006 2.009 2.358 hash_to_proc 0.981 0.973 1.027 hash_values 2.817 2.790 2.823 vm2_bighash* 2.423 2.180 3.264 1.33519 1.33252 1.44648 ``` I used the following script on 4.2GHz i7-4790K for this: ``` ruby ../ruby/benchmark/driver.rb -p hash -r 3 -e trunk::trunk/miniruby -e yura::yura/miniruby -e yura::yura64/miniruby -e current::./miniruby 2>/dev/n\ ull|awk 'NF==4 && /hash/ {s1+=$2;s2+=$3;s3+=$4;n++;print} END{print s1/n, s2/n, s3/n}' ``` You wrote **"I agree to determine the implementation with coin toss"** in your report. I think it is better not do this. My implementation is the original one. Yura just repeated my major ideas: putting elements in array, open hash addressing (although he fiercely arguing with me a lot that the buckets are better), using weaker hash function when there is no supension of a collision attack. I did not use any his ideas. In fact I stopped to improve my tables in April, Yura produced his latest variant in September (btw it would be interesting to see also comparison of his other two variants with buckets he proposed in July. I put some such comparison on https://github.com/vnmakarov/ruby/blob/hash_tables_with_open_addressing/README.md). I believed the competition was unhealthy and it seems I was right as Yura spent his time on his implementation and you had to spend your time on your thorough investigation and still you need "a coin toss" to decide. I'd like to propose a plan which is to use my code as the base and Yura can add his own original code later: o fixing Murmur hash in MRI o different hash tables growth rate (it needs performance evaluation) o smaller hash table header (usually it is accessed randomly and my header is just one cache line, further size decreasing hardly improves performance, imho) o statistical collision attack recognition (i doubt it will improves performance as the surrounded code is memory bound) Again this competition was unhealthy at least for me. I could have spent more time on more serious MRI performance improvement. I'll respect any your decision, it will be enough for me that all my major ideas about MRI hash tables is used. ---------------------------------------- Feature #12142: Hash tables with open addressing https://bugs.ruby-lang.org/issues/12142#change-61178 * Author: Vladimir Makarov * Status: Open * Priority: Normal * Assignee: ---------------------------------------- ~~~ Hello, the following patch contains a new implementation of hash tables (major files st.c and include/ruby/st.h). Modern processors have several levels of cache. Usually,the CPU reads one or a few lines of the cache from memory (or another level of cache). So CPU is much faster at reading data stored close to each other. The current implementation of Ruby hash tables does not fit well to modern processor cache organization, which requires better data locality for faster program speed. The new hash table implementation achieves a better data locality mainly by o switching to open addressing hash tables for access by keys. Removing hash collision lists lets us avoid *pointer chasing*, a common problem that produces bad data locality. I see a tendency to move from chaining hash tables to open addressing hash tables due to their better fit to modern CPU memory organizations. CPython recently made such switch (https://hg.python.org/cpython/file/ff1938d12240/Objects/dictobject.c). PHP did this a bit earlier https://nikic.github.io/2014/12/22/PHPs-new-hashtable-implementation.html. GCC has widely-used such hash tables (https://gcc.gnu.org/svn/gcc/trunk/libiberty/hashtab.c) internally for more than 15 years. o removing doubly linked lists and putting the elements into an array for accessing to elements by their inclusion order. That also removes pointer chaising on the doubly linked lists used for traversing elements by their inclusion order. A more detailed description of the proposed implementation can be found in the top comment of the file st.c. The new implementation was benchmarked on 21 MRI hash table benchmarks for two most widely used targets x86-64 (Intel 4.2GHz i7-4790K) and ARM (Exynos 5410 - 1.6GHz Cortex-A15): make benchmark-each ITEM=bm_hash OPTS='-r 3 -v' COMPARE_RUBY='' Here the results for x86-64: hash_aref_dsym 1.094 hash_aref_dsym_long 1.383 hash_aref_fix 1.048 hash_aref_flo 1.860 hash_aref_miss 1.107 hash_aref_str 1.107 hash_aref_sym 1.191 hash_aref_sym_long 1.113 hash_flatten 1.258 hash_ident_flo 1.627 hash_ident_num 1.045 hash_ident_obj 1.143 hash_ident_str 1.127 hash_ident_sym 1.152 hash_keys 2.714 hash_shift 2.209 hash_shift_u16 1.442 hash_shift_u24 1.413 hash_shift_u32 1.396 hash_to_proc 2.831 hash_values 2.701 The average performance improvement is more 50%. ARM results are analogous -- no any benchmark performance degradation and about the same average improvement. The patch can be seen as https://github.com/vnmakarov/ruby/compare/trunk...hash_tables_with_open_addressing.patch or in a less convenient way as pull request changes https://github.com/ruby/ruby/pull/1264/files This is my first patch for MRI and may be my proposal and implementation have pitfalls. But I am keen to learn and work on inclusion of this code into MRI. ~~~ ---Files-------------------------------- 0001-st.c-change-st_table-implementation.patch (59.4 KB) st-march31.patch (114 KB) base.patch (93.8 KB) hash.patch (4.48 KB) strong_hash.patch (8.08 KB) city.patch (19.4 KB) new-hash-table-benchmarks.patch (1.34 KB) hash_improvements_and_st_implementation_changes.mbox (101 KB) hash_improvements_and_st_array_with_open_addressing.mbox (108 KB) -- https://bugs.ruby-lang.org/ Unsubscribe: