[ruby-core:95036] [Ruby master Bug#16007] Process.clock_getres matches the clock in practice for Process::CLOCK_{PROCESS, THREAD}_CPUTIME_ID FAILED fails on armv7hl

Issue #16007 has been updated by Eregon (Benoit Daloze).


vo.x (Vit Ondruch) wrote:
> However, I wonder if there is some explanation for disabling the test. I see a lot of comments such as `# These clocks in practice on Linux do not seem to match their reported resolution.` or `# These clocks in practice on ARM on Linux do not seem to match their reported resolution.` but that is strange. Why they should be? Is that known limitation of Linux or some HW? I would be interested to know.

My understanding is those are all operating system (or maybe hardware) bugs.
It seems operating systems don't bother testing clock_getres() much, and as a result I would recommend to never use it.

Also see https://github.com/copiousfreetime/hitimes/pull/73#discussion_r287894886 for one usage I know of.

> The point is that I don't understand what would be the point of such API if the results can't be trusted ...

Maybe we should remove Process.clock_getres() since it's so frequently inconsistent with clock_gettime()?

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Bug #16007: Process.clock_getres matches the clock in practice for Process::CLOCK_{PROCESS,THREAD}_CPUTIME_ID FAILED fails on armv7hl
https://bugs.ruby-lang.org/issues/16007#change-81667

* Author: vo.x (Vit Ondruch)
* Status: Assigned
* Priority: Normal
* Assignee: Eregon (Benoit Daloze)
* Target version: 
* ruby -v: ruby 2.7.0dev (2019-07-15T10:39:47Z master 0c6c937904) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
During build of Ruby 2.7.0 0c6c937904 on Fedora Rawhide, I observe following test failure on armv7hl (other arches are fine):

~~~
1)
Process.clock_getres matches the clock in practice for Process::CLOCK_PROCESS_CPUTIME_ID FAILED
Expected 10000
 not to equal 10000
/builddir/build/BUILD/ruby-2.7.0-0c6c937904/spec/ruby/core/process/clock_getres_spec.rb:30:in `block (4 levels) in <top (required)>'
/builddir/build/BUILD/ruby-2.7.0-0c6c937904/spec/ruby/core/process/clock_getres_spec.rb:4:in `<top (required)>'
2)
Process.clock_getres matches the clock in practice for Process::CLOCK_THREAD_CPUTIME_ID FAILED
Expected 10000
 not to equal 10000
/builddir/build/BUILD/ruby-2.7.0-0c6c937904/spec/ruby/core/process/clock_getres_spec.rb:30:in `block (4 levels) in <top (required)>'
/builddir/build/BUILD/ruby-2.7.0-0c6c937904/spec/ruby/core/process/clock_getres_spec.rb:4:in `<top (required)>'
Finished in 189.216527 seconds
3770 files, 30971 examples, 112151 expectations, 2 failures, 0 errors, 0 tagged
~~~

I did not observe such issue previously testing with d9f8b88b47



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