But this will find 3,000,000 over six times in a second:

use strict;
use warnings;
use feature 'say';
use Benchmark qw/timethis/;

use Inline 'C';

my $search_to = 3000000;

timethis -10, \&eratos_inline_c;

# Thin wrapper to bind input params for the benchmark.
sub eratos_inline_c {
    return @{inline_c_pa_eratos_primes( $search_to )};
}


__DATA__

__C__


/* Find all primes up to 'search_to' using the Sieve of Eratosthenes. 
+*/
AV * inline_c_pa_eratos_primes ( int search_to ) 
{
    AV* av = newAV();
    int* primes = 0;
    int i;
    Newx( primes, search_to + 1 , int );
    if( ! primes ) croak( "Failed to allocate memory.\n" );
    for( i = 0; i <= search_to; i++ ) primes[i] = 1;
    for( i = 2; i * i <= search_to; i++ ) 
    {
        if( primes[i] ) 
        {
            int j;
            for( j = i; j * i <= search_to; j++ ) primes[ i * j ] = 0;
        }
    }
    for( i = 2; i <= search_to; i++ ) 
    {
        if( primes[i] == 1 ) av_push( av, newSViv( i ) );
    }
    Safefree( primes );
    return sv_2mortal( av );
}
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