From @eserte

This is a bug report for perl from slaven@​rezic.de,
generated with the help of perlbug 1.41 running under perl 5.29.9.

The test suite of Linux-GetPidstat-0.09 fails since perl 5.29.2​:

# Failed test at t/08_collector_parser.t line 47.
# Structures begin differing at​:
# $got->{memory_percent} = '42.14'
# $expected->{memory_percent} = '42.15'
# {
# 'cpu' => '42.48',
# 'cswch_per_sec' => '33.54',
# 'disk_read_per_sec' => '500',
# 'disk_write_per_sec' => '-500',
# 'memory_percent' => '42.14',
# 'memory_rss' => '13532901250',
# 'nvcswch_per_sec' => '44.04',
# 'stk_ref' => '39500',
# 'stk_size' => '190000'
# }
# Looks like you failed 1 test of 5.
t/08_collector_parser.t ..
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/5 subtests

This looks like floating point inaccuracy, but inequality
happens already with two digits after the dot.

Flags​:
  category=core
  severity=low

Site configuration information for perl 5.29.9​:

Configured by eserte at Thu Mar 21 21​:10​:55 UTC 2019.

Summary of my perl5 (revision 5 version 29 subversion 9) configuration​:
 
  Platform​:
  osname=linux
  osvers=4.15.0-46-generic
  archname=x86_64-linux
  uname='linux ubuntu18 4.15.0-46-generic #49-ubuntu smp wed feb 6 09​:33​:07 utc 2019 x86_64 x86_64 x86_64 gnulinux '
  config_args='-ds -e -Dprefix=/opt/perl-5.29.9 -Dusedevel -Dusemallocwrap=no -Dcf_email=srezic@​cpan.org'
  hint=recommended
  useposix=true
  d_sigaction=define
  useithreads=undef
  usemultiplicity=undef
  use64bitint=define
  use64bitall=define
  uselongdouble=undef
  usemymalloc=n
  default_inc_excludes_dot=define
  bincompat5005=undef
  Compiler​:
  cc='cc'
  ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
  optimize='-O2'
  cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
  ccversion=''
  gccversion='7.3.0'
  gccosandvers=''
  intsize=4
  longsize=8
  ptrsize=8
  doublesize=8
  byteorder=12345678
  doublekind=3
  d_longlong=define
  longlongsize=8
  d_longdbl=define
  longdblsize=16
  longdblkind=3
  ivtype='long'
  ivsize=8
  nvtype='double'
  nvsize=8
  Off_t='off_t'
  lseeksize=8
  alignbytes=8
  prototype=define
  Linker and Libraries​:
  ld='cc'
  ldflags =' -fstack-protector-strong -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/7/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
  libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc
  perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  libc=libc-2.27.so
  so=so
  useshrplib=false
  libperl=libperl.a
  gnulibc_version='2.27'
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs
  dlext=so
  d_dlsymun=undef
  ccdlflags='-Wl,-E'
  cccdlflags='-fPIC'
  lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'

@​INC for perl 5.29.9​:
  /opt/perl-5.29.9/lib/site_perl/5.29.9/x86_64-linux
  /opt/perl-5.29.9/lib/site_perl/5.29.9
  /opt/perl-5.29.9/lib/5.29.9/x86_64-linux
  /opt/perl-5.29.9/lib/5.29.9

Environment for perl 5.29.9​:
  HOME=/home/eserte
  LANG=en_US.UTF-8
  LANGUAGE (unset)
  LC_ALL=de_DE.UTF-8
  LD_LIBRARY_PATH (unset)
  LOGDIR (unset)
  PATH=/usr/local/bin​:/usr/bin​:/bin​:/usr/local/sbin​:/usr/sbin​:/sbin​:/home/eserte/bin/linux-gnu​:/home/eserte/bin/sh​:/home/eserte/bin​:/home/eserte/bin/pistachio-perl/bin​:/usr/games​:/home/eserte/devel
  PERLDOC=-MPod​::Perldoc​::ToTextOverstrike
  PERL_BADLANG (unset)
  SHELL=/usr/bin/zsh

From @jkeenan

On Sun, 24 Mar 2019 09​:55​:16 GMT, slaven@​rezic.de wrote​:

This is a bug report for perl from slaven@​rezic.de,
generated with the help of perlbug 1.41 running under perl 5.29.9.

-----------------------------------------------------------------
The test suite of Linux-GetPidstat-0.09 fails since perl 5.29.2​:

# Failed test at t/08_collector_parser.t line 47.
# Structures begin differing at​:
# $got->{memory_percent} = '42.14'
# $expected->{memory_percent} = '42.15'
# {
# 'cpu' => '42.48',
# 'cswch_per_sec' => '33.54',
# 'disk_read_per_sec' => '500',
# 'disk_write_per_sec' => '-500',
# 'memory_percent' => '42.14',
# 'memory_rss' => '13532901250',
# 'nvcswch_per_sec' => '44.04',
# 'stk_ref' => '39500',
# 'stk_size' => '190000'
# }
# Looks like you failed 1 test of 5.
t/08_collector_parser.t ..
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/5 subtests

This looks like floating point inaccuracy, but inequality
happens already with two digits after the dot.

This module has a ton of prerequisites, but the problem ultimately has nothing to do with either Linux or PID statistics. Bisection -- on FreeBSD! -- with attached program 133953-pid.pl, pointed to this commit​:

#####
ce6f496 is the first bad commit
commit ce6f496
Author​: sisyphus <sisyphus1@​optusnet.com.au>
Date​: Wed Aug 1 22​:33​:38 2018 +1000

PATCH​: [perl #41202] text->float gives wrong answer

This changes to use Perl_strtod() when available, and that
turns out to be the key to fixing this bug.

S_mulexp10() is removed from embed.fnc to avoid repeating
the complicated prerequisites for defining Perl_strtod().
This works because this static function already was defined
before use in numeric.c, and always called in full form
without using a macro.
#####

I was ultimately able to further reduce it to attached program y133953.pl and reconfirm the breaking commit.

However, given that the commit in question fixed a bug in perl, we should reject this ticket and advise the downstream CPAN maintainer to revise his test data.

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

From @jkeenan

133953-pid.pl

From @jkeenan

y133953.pl

The RT System itself - Status changed from 'new' to 'open'

From @tonycoz

On Sun, 24 Mar 2019 08​:30​:57 -0700, jkeenan wrote​:

On Sun, 24 Mar 2019 09​:55​:16 GMT, slaven@​rezic.de wrote​:

This is a bug report for perl from slaven@​rezic.de,
generated with the help of perlbug 1.41 running under perl 5.29.9.

-----------------------------------------------------------------
The test suite of Linux-GetPidstat-0.09 fails since perl 5.29.2​:

# Failed test at t/08_collector_parser.t line 47.
# Structures begin differing at​:
# $got->{memory_percent} = '42.14'
# $expected->{memory_percent} = '42.15'
# {
# 'cpu' => '42.48',
# 'cswch_per_sec' => '33.54',
# 'disk_read_per_sec' => '500',
# 'disk_write_per_sec' => '-500',
# 'memory_percent' => '42.14',
# 'memory_rss' => '13532901250',
# 'nvcswch_per_sec' => '44.04',
# 'stk_ref' => '39500',
# 'stk_size' => '190000'
# }
# Looks like you failed 1 test of 5.
t/08_collector_parser.t ..
Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/5 subtests

This looks like floating point inaccuracy, but inequality
happens already with two digits after the dot.

This module has a ton of prerequisites, but the problem ultimately has
nothing to do with either Linux or PID statistics. Bisection -- on
FreeBSD! -- with attached program 133953-pid.pl, pointed to this
commit​:

#####
ce6f496 is the first bad commit
commit ce6f496
Author​: sisyphus <sisyphus1@​optusnet.com.au>
Date​: Wed Aug 1 22​:33​:38 2018 +1000

PATCH​: [perl #41202] text->float gives wrong answer

This changes to use Perl_strtod() when available, and that
turns out to be the key to fixing this bug.

S_mulexp10() is removed from embed.fnc to avoid repeating
the complicated prerequisites for defining Perl_strtod().
This works because this static function already was defined
before use in numeric.c, and always called in full form
without using a macro.
#####

I was ultimately able to further reduce it to attached program
y133953.pl and reconfirm the breaking commit.

However, given that the commit in question fixed a bug in perl, we
should reject this ticket and advise the downstream CPAN maintainer to
revise his test data.

Thank you very much.

Leaving the rounding to the final step would help too.

If I add some debug output to _mean​:

mean 34.62 34.62 34.65 34.65 => 34.635 => 34.63
mean 7.33 7.33 7.59 7.81 => 7.515 => 7.51

The second last number is the raw mean, the last number the rounded value.

Rounding at this point simply accumulates errors.

If you remove the rounding in _mean and do it only as the final step the result is the expected value.

Tony

From @jkeenan

The author of Linux​::GetPidstat released a new version to CPAN in late March which addresses the issues raised in this ticket.

Marking this ticket Resolved.
--
James E Keenan (jkeenan@​cpan.org)

@jkeenan - Status changed from 'open' to 'resolved'