Ruby

Assigning to kosaki since he wrote the current GVL.
I'm hoping single-core vm_thread_pass benchmark can be
improved, but I'm not sure...

Using bare, Linux-specific futexes instead of relying on NPTL-provided primitives seems to offer some speedups in the more realistic benchmarks which release GVL for IO. Performance seems stable between multi-core and single-core benchmarks. However, there is still more regressions for single-core systems, but I think it mainly affects esoteric cases. Mainly, the io_pipe_rw and vm_thread_pipe benchmarks are improved across the board, so I am pretty happy with that. Some of the performance changes (good or bad) may also be the result of size reductions between the 40-byte NPTL mutex and the 4 byte futex shifting data into a different cache line. io and thread '-p (_io_|thread)' benchmark results on an AMD FX-8320 @ 3.5GHz: io_copy_stream_write 1.040 io_copy_stream_write_socket 1.027 io_file_create 1.016 io_file_read 1.057 io_file_write 1.001 io_nonblock_noex 1.047 io_nonblock_noex2 1.037 io_pipe_rw 1.077 io_select 1.024 io_select2 1.003 io_select3 0.991 require_thread 8.379 vm_thread_alive_check1 1.171 vm_thread_close 1.015 vm_thread_condvar1 0.979 vm_thread_condvar2 1.192 vm_thread_create_join 1.043 vm_thread_mutex1 0.985 vm_thread_mutex2 1.005 vm_thread_mutex3 0.991 vm_thread_pass 4.563 vm_thread_pass_flood 0.991 vm_thread_pipe 1.867 vm_thread_queue 0.995 vm_thread_sized_queue 1.050 vm_thread_sized_queue2 1.079 vm_thread_sized_queue3 1.073 vm_thread_sized_queue4 1.087 single core (schedtool -a 0x1 -e ...): io_copy_stream_write 1.039 io_copy_stream_write_socket 1.012 io_file_create 1.010 io_file_read 1.066 io_file_write 0.999 io_nonblock_noex 1.061 io_nonblock_noex2 1.020 io_pipe_rw 1.101 io_select 1.008 io_select2 1.001 io_select3 0.992 require_thread 1.005 vm_thread_alive_check1 0.938 vm_thread_close 1.135 vm_thread_condvar1 1.145 vm_thread_condvar2 1.134 vm_thread_create_join 1.146 vm_thread_mutex1 0.999 vm_thread_mutex2 0.999 vm_thread_mutex3 1.001 vm_thread_pass 0.887 vm_thread_pass_flood 0.973 vm_thread_pipe 1.100 vm_thread_queue 1.013 vm_thread_sized_queue 1.125 vm_thread_sized_queue2 1.172 vm_thread_sized_queue3 1.184 vm_thread_sized_queue4 1.081