Use Ruby's Etc.nprocessors for processor_count if available #814
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MRI has had Etc.nprocessors since Ruby 2.2, which uses: - sched_getaffinity(): Linux - sysconf(_SC_NPROCESSORS_ONLN): GNU/Linux, NetBSD, FreeBSD, OpenBSD, DragonFly BSD, OpenIndiana, Mac OS X, AIX - GetSystemInfo(): Win32 This should be faster than the alternatives of reading from /proc/cpuinfo, using WIN32OLE, or spawning a new process. This also has the advantage of reporting processor count based on CPU affinity which /usr/bin/nproc did, but reading /proc/cpuinfo does not. When using this value for controlling the level of parallelism, we should ideally be using the processes CPU affinity.
Contributor
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$ ruby -r rubygems -r etc -e 'puts Etc.nprocessors' (4 is the correct answer for this machine) $ ruby -v $ uname -a |
graaff
reviewed
Jul 7, 2019
| def compute_processor_count | ||
| if Concurrent.on_jruby? | ||
| java.lang.Runtime.getRuntime.availableProcessors | ||
| elsif defined?(Etc) && Etc.respond_to?(:nprocessors) && (nprocessor = Etc.nprocessors rescue nil) |
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Etc is not included by default, so should this probe also include a require "etc"?
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👍 Good catch. I added it as a top-level require (I believe all supported rubies should support etc, older ones just don't implement nprocessors).
pitr-ch
added
the
enhancement
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In 0371ed4 from the discussions in #576, we switched the default method of detecting processor count from
/usr/bin/nprocto reading/proc/cpuinfo. This avoids a fork, but means that we no longer respect CPU affinity, which we should want if using this value to control parallelism. I imagine it should work on Alpha too.MRI has had
Etc.nprocessorssince Ruby 2.2, which uses:This should be faster than the alternatives of reading from
/proc/cpuinfo, using WIN32OLE, or spawning a new process (though all should be plenty fast since this is memoized). It also will take into account CPU affinity.Before:
After:
cc @pitr-ch @matthewd @graaff