On aarch64/Power64 it seems tcp fastopen isn't properly detected. All the builders for these arches are running Fedora 23 with a 4.4.x kernel. This kernel feature was enabled by default from 3.13 [1]. Seems a regression/change in 2.9.3 as it built OK in older versions.

http://arm.koji.fedoraproject.org/koji/packageinfo?packageID=13036
http://ppc.koji.fedoraproject.org/koji/packageinfo?packageID=12938

[1] http://kernelnewbies.org/Linux_3.13#head-159ff61ea3acfd67b88855e75dbbb140f8825c4a


Loaded suite -e
Started
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....................F
===============================================================================
Failure: test_wait_writable_timed(TestDefaultWait)
/builddir/build/BUILD/rubygem-kgio-2.9.3/usr/share/gems/gems/kgio-2.9.3/test/test_default_wait.rb:43:in `test_wait_writable_timed'
     40:     assert_in_delta diff, 1.1, 0.2
     41: 
     42:     a.kgio_read(16384)
  => 43:     assert_equal b, b.kgio_wait_writable(1.1)
     44:   end
     45: end
<#<Kgio::Pipe:fd 83>> expected but was
<nil>
diff:
? #<Kgio::Pipe:fd 83>
? n    l             
===============================================================================
...............................................................................
..................................................TCP Fast Open not enabled on this system (check kernel docs)
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Finished in 345.134266687 seconds.
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365 tests, 11776446 assertions, 1 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
99.726% passed