Re: grep extremely slow on OSX

[Paolo Bonzini]

On 02/06/2010 06:25 PM, Titus von der Malsburg wrote:
> On Sat, Feb 6, 2010 at 4:54 PM, Paolo Bonzini<address@hidden>  wrote:
> > Can you try with 2.5.4 on Linux, but configuring with --with-included-regex?
>
> Then it takes 19min.  When I do the same on OSX it takes again 12 min.

That's more or less the same ratio for your hand-crafted program, so it 
means it is the same performance apart from the CPU speed.

> Does this mean that the Berkley implementation of regex on OSX is
> crappy and that grep therefore uses it's own engine?  Is there a way
> to build grep with the GNU engine on OSX?

It means we identified the culprit (the regex engine; possibly the 
strcoll/wcscoll calls used to handle [0-9]), but it is still strange 
because, AFAICT, the regex code should not even be invoked unless you 
use grep -o or --color or similar options.  Instead, grep should use its 
own DFA implementation.

Running under LC_ALL=C should mitigate or eliminate the bad performance.

Paolo