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Bug #20157

closed

Regression in GC.measure_total_time

Added by rianmcguire (Rian McGuire) 10 months ago. Updated 9 months ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-linux]
Backport:
3.0: DONTNEED, 3.1: DONTNEED, 3.2: DONTNEED, 3.3: DONE
[ruby-core:116045]

Description

Setting GC.measure_total_time = false is no longer disabling GC time measurement in Ruby 3.3.0.

Reproduction script:

puts RUBY_DESCRIPTION

GC.measure_total_time = false

puts "measure_total_time is now false"
puts "GC.stat(:time) = #{GC.stat(:time)}"
puts "There should be no further clock_gettime syscalls"

# Generate some garbage
Random.new.bytes(100 * 1024 * 1024)
GC.start

puts "GC.stat(:time) = #{GC.stat(:time)}. This should be unchanged from above"

Ruby 3.2.2 (expected behaviour):

$ strace --trace=clock_gettime --signal=none ruby --disable-gems bug.rb    
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=45735959}) = 0
ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x86_64-linux]
measure_total_time is now false
GC.stat(:time) = 0
There should be no further clock_gettime syscalls
GC.stat(:time) = 0. This should be unchanged from above
+++ exited with 0 +++

Ruby 3.3.0:

$ strace --trace=clock_gettime --signal=none ruby --disable-gems bug.rb    
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=31784505}) = 0
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-linux]
measure_total_time is now false
GC.stat(:time) = 0
There should be no further clock_gettime syscalls
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=47132055}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=47576566}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=47586656}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=47852906}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=180726043}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=181242023}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=181248873}) = 0
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=191276005}) = 0
GC.stat(:time) = 11. This should be unchanged from above
+++ exited with 0 +++

It appears that this was caused by commit https://github.com/ruby/ruby/commit/93ac7405b80cc61930d73da04441fa09af1851e1 -- the test for MEASURE_GC inside in gc_enter_event_measure_p was lost in the refactoring.

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