Re: [perl #38179] -X _ is 20% slower than -X; Fcntl S_ISDIR is 9times slower than -d

On Sat, 07 Jan 2006 10:12:40 -0800
"Nicholas Clark via RT" <perlbug-followup@perl.org> wrote:

>Your conclusion about _ not being fast is not valid. The _ handle is
>documented as re-using the last stat test. However, your comparison
>tests are:
>
>>             "-d"                 => '{$r = -d "test"}',
>>             "_"                  => '{stat "test"; $r = -d _}',
>
>"-d" will perform one stat system call and then the -d test, using 1
>perl op. "_" will perform one stat system call and then the -d test,
>using 2 perl ops.

Yes, I know.  It just seems a bit odd that the extra operation takes
enough work for the two tests to not be exactly equivalent.

>I feel that your tests are somewhat unfair, in that the calls to Fcntl
>incur subroutine call overhead, whereas your code is all inline.
>
>If I change the tests so that all are calling subroutines:
>then a different pattern emerges.
>
>To me, this suggests that with the constants now inlined inside Fcntl,
>S_ISDIR() now is comparable in speed with an equivalent local
>subroutine.

The point of writing the tests as they were is that each represents how
their methods would be used when speed is an issue.  In Fcntl, a sub
call is unavoidable; in the other tests, it's unnecessary.

>Note that the two tests Fcntl and Fcntl_only will be slower than they
>might at first seem, because &Fcntl::S_IFMT is not an inlinable
>constant, so always has to be called:
>
>sub S_IFMT  { @_ ? ( $_[0] & _S_IFMT() ) : _S_IFMT()  }

Does this serve a useful purpose?  With sub calls so expensive, it would
be much better for S_IFMT to be a constant, leaving the masking to the
end users.  It's strange for this extra functionality to exist in a
module that's supposed to be a translation of fcntl.h.

• [perl #38179] -X _ is 20% slower than -X; Fcntl S_ISDIR is 9 times slower than -d by Tels
• Re: [perl #38179] -X _ is 20% slower than -X; Fcntl S_ISDIR is 9times slower than -d by R.K.
• [perl #38179] -X _ is 20% slower than -X; Fcntl S_ISDIR is 9 times slower than -d by R.K.
• Re: [perl #38179] -X _ is 20% slower than -X; Fcntl S_ISDIR is 9 times slower than -d by Nicholas Clark