Dev Builds » 20181127-0739

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NCM plays each Stockfish dev build 20,000 times against Stockfish 14. This yields an approximate Elo difference and establishes confidence in the strength of the dev builds.


Host Duration Avg Base NPS Games WLD Standard Elo Ptnml(0-2) Gamepair Elo

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ID Host Base NPS Games WLD Standard Elo Ptnml(0-2) Gamepair Elo CLI PGN


Commit ID de7182f4eee33029a7b79f6b097db06357669127
Author Steinar H. Gunderson
Date 2018-11-27 07:39:23 UTC
Turn on MADV_RANDOM for Syzygy mmaps (on Unix-like builds) When running on a cloud VM (n1-highcpu-96) with several NVMe SSDs and some non-SSDs for tablebases, I noticed that the average SSD request size was more than 256 kB. This doesn't make a lot of sense for Syzygy tablebases, which have a block size of 32 bytes and very low locality. Seemingly, the tablebase access patterns during probing make the OS, at least Linux, think that readahead is advantageous; normally, it gives up doing readahead if there are too many misses, but it doesn't, perhaps due to the fairly high overall hit rates. (It seems the kernel cannot distinguish between reading a block that was paged in because the userspace wanted it explicitly, and one that was read as part of readahead.) Setting MADV_RANDOM effectively turns off readahead, which causes the request size to drop to 4 kB. In the aforemented cloud VM test, this roughly tripled the amount of I/O requests that were able to go through, while reducing the total traffic from 2.8 GB/sec to 56 MB/sec (moving the bottleneck to the non-SSDs; it seems the SSDs could have sustained many more requests). Closes No functional change.
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