linux-kernel - Re: get_maintainer.pl produces non-deterministic results

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Date:   Wed, 11 Dec 2019 16:12:44 -0800
From:   Joe Perches <joe@...ches.com>
To:     Vegard Nossum <vegard.nossum@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: get_maintainer.pl produces non-deterministic results

On Wed, 2019-12-11 at 07:41 +0100, Vegard Nossum wrote:
> On Wed, 11 Dec 2019 at 01:02, Joe Perches <joe@...ches.com> wrote:
> > On Tue, 2019-12-10 at 14:47 +0100, Dmitry Vyukov wrote:
> > > Hi Joe,
> > > 
> > > scripts/get_maintainer.pl fs/proc/task_mmu.c
> > > non-deterministically gives me from 13 to 16 results, different number
> > > every time (on upstream 6794862a). Perl v5.28.1. Michael confirmed
> > > this with v5.28.2.
> > > Vergard suggested to check PERL_HASH_SEED=0. Indeed it fixes
> > > non-determinism. But I guess it's not the right solution, there should
> > > be some logical problem.
> > > My perl-fo is weak, I appreciate if somebody with proper perl-fo takes a look.
> > > 
> > > Thanks
> > 
> > https://lkml.org/lkml/2017/7/13/789
> 
> Right, so you can make it reproducible if you add a tie-break to the sorting:
> 
> diff --git a/scripts/get_maintainer.pl b/scripts/get_maintainer.pl
> index 34085d146fa2c..109d9fb134dad 100755
> --- a/scripts/get_maintainer.pl
> +++ b/scripts/get_maintainer.pl
> @@ -2179,7 +2179,7 @@ sub vcs_assign {
>      $hash{$_}++ for @lines;
> 
>      # sort -rn
> -    foreach my $line (sort {$hash{$b} <=> $hash{$a}} keys %hash) {
> +    foreach my $line (sort {$hash{$b} <=> $hash{$a} || $a cmp $b} keys %hash) {
>         my $sign_offs = $hash{$line};
>         my $percent = $sign_offs * 100 / $divisor;
> 
> This would actually favour names that start with early letters (A, B,
> ...) over late letters (..., Y, Z), which might also be a bad thing. I
> think to fix that you could include everybody who has the same number
> of signoffs at the cutoff:
> 
> diff --git a/scripts/get_maintainer.pl b/scripts/get_maintainer.pl
> index 34085d146fa2c..80d3ed2ee6d70 100755
> --- a/scripts/get_maintainer.pl
> +++ b/scripts/get_maintainer.pl
> @@ -2179,7 +2179,8 @@ sub vcs_assign {
>      $hash{$_}++ for @lines;
> 
>      # sort -rn
> -    foreach my $line (sort {$hash{$b} <=> $hash{$a}} keys %hash) {
> +    my $prev_sign_offs = -1;
> +    foreach my $line (sort {$hash{$b} <=> $hash{$a} || $a cmp $b} keys %hash) {
>         my $sign_offs = $hash{$line};
>         my $percent = $sign_offs * 100 / $divisor;
> 
> @@ -2187,7 +2188,7 @@ sub vcs_assign {
>         next if (ignore_email_address($line));
>         $count++;
>         last if ($sign_offs < $email_git_min_signatures ||
> -                $count > $email_git_max_maintainers ||
> +                ($prev_sign_offs != $sign_offs && $count >
> $email_git_max_maintainers) ||
>                  $percent < $email_git_min_percent);
>         push_email_address($line, '');
>         if ($output_rolestats) {
> @@ -2196,6 +2197,8 @@ sub vcs_assign {
>         } else {
>             add_role($line, $role);
>         }
> +
> +       $prev_sign_offs = $sign_offs;
>      }
>  }
> 
> These patches are probably horribly whitespace damaged, hopefully you
> get the gist of it though...

I get the gist, but I think it's also not particularly important
to be repeatable.  I think it's more important to get more pattern
coverage of the MAINTAINERS file as that is more important than
any use of git history.