Issue #20902 has been reported by ioquatix (Samuel Williams). ---------------------------------------- Feature #20902: Allow `IO::Buffer#copy` to release the GVL. https://bugs.ruby-lang.org/issues/20902 * Author: ioquatix (Samuel Williams) * Status: Open ---------------------------------------- Related to <https://bugs.ruby-lang.org/issues/20876>. ## Background `IO::Buffer#copy` execution time is proportional to the length of the data copied. As such, large copies can take a long time (100ms+). Currently, the GVL is not released, which can stall the Ruby interpreter. ## Proposal Pull Request: https://github.com/ruby/ruby/pull/12021 If the size of the data to be copied is larger than a specific amount (heuristic), we will perform `memmove` using `rb_nogvl`. The initial size heuristic is set to 1MiB. This won't be perfect for every system, but should be good enough to avoid ms+ stalls. ## Results I measured the difference: | GVL | Threads | Buffer Size | Total Duration | Throughput (MB/s) | |-----|---------|-------------|----------------|-------------------| | Yes | 1 | 1 | 0.12ms | 8393.09 | | Yes | 1 | 5 | 0.51ms | 9857.7 | | Yes | 1 | 10 | 1.12ms | 8937.54 | | Yes | 1 | 20 | 2.22ms | 9015.95 | | Yes | 2 | 1 | 0.24ms | 8307.07 | | Yes | 2 | 5 | 1.13ms | 8819.58 | | Yes | 2 | 10 | 1.49ms | 13385.35 | | Yes | 2 | 20 | 5.63ms | 7110.8 | | Yes | 4 | 1 | 0.92ms | 4360.18 | | Yes | 4 | 5 | 2.08ms | 9606.58 | | Yes | 4 | 10 | 4.51ms | 8863.13 | | Yes | 4 | 20 | 9.3ms | 8601.41 | | Yes | 8 | 1 | 1.22ms | 6574.93 | | Yes | 8 | 5 | 3.56ms | 11239.27 | | Yes | 8 | 10 | 7.31ms | 10943.68 | | Yes | 8 | 20 | 15.57ms | 10274.99 | | Yes | 16 | 1 | 1.95ms | 8220.16 | | Yes | 16 | 5 | 5.51ms | 14518.05 | | Yes | 16 | 10 | 13.77ms | 11618.96 | | Yes | 16 | 20 | 27.21ms | 11759.43 | | Yes | 32 | 1 | 3.24ms | 9891.05 | | Yes | 32 | 5 | 11.42ms | 14007.41 | | Yes | 32 | 10 | 21.64ms | 14786.48 | | Yes | 32 | 20 | 45.52ms | 14060.25 | | No | 1 | 1 | 0.13ms | 7582.85 | | No | 1 | 5 | 0.44ms | 11248.55 | | No | 1 | 10 | 1.11ms | 9029.91 | | No | 1 | 20 | 2.43ms | 8228.42 | | No | 2 | 1 | 0.18ms | 11245.61 | | No | 2 | 5 | 0.96ms | 10396.76 | | No | 2 | 10 | 1.9ms | 10501.59 | | No | 2 | 20 | 3.16ms | 12656.77 | | No | 4 | 1 | 0.69ms | 5827.76 | | No | 4 | 5 | 1.15ms | 17440.54 | | No | 4 | 10 | 2.31ms | 17307.79 | | No | 4 | 20 | 4.11ms | 19483.68 | | No | 8 | 1 | 0.67ms | 11954.1 | | No | 8 | 5 | 1.3ms | 30713.68 | | No | 8 | 10 | 2.05ms | 38990.98 | | No | 8 | 20 | 4.15ms | 38552.37 | | No | 16 | 1 | 0.96ms | 16698.03 | | No | 16 | 5 | 1.46ms | 54782.47 | | No | 16 | 10 | 2.74ms | 58295.64 | | No | 16 | 20 | 4.89ms | 65482.43 | | No | 32 | 1 | 1.82ms | 17554.27 | | No | 32 | 5 | 2.68ms | 59673.59 | | No | 32 | 10 | 3.87ms | 82733.34 | | No | 32 | 20 | 6.93ms | 92297.47 | In the base case, the performance is about the same, but in the best case, the throughput is significantly better: 15GiB/s vs 92GiB/s (32 threads copying 20MiB of data). -- https://bugs.ruby-lang.org/