Portal Flow calculates which vis-leaves are touching and also which vis-leaves can see into other vis-leaves. It can often take a long time it your map is large, or simply has a large amount of vis-leaves, because the time taken to calculate increases exponentially with the amount of vis-leaves.

If you want to reduce the time it takes, then you will need to optimize your map. This guide should help:

Zombie's Optimization Guide

I have the same problem. I've now been compiling for over 24 hours and it's still jammed on ''Portal Flow''. I have optimized my map ( putted nodraw to a lot of places and all that) but it's still doing that. Weird.

Labbis, Optimization is alot more then just putting nodraw on the unseen surfaces. Did you go through and make small brushes into func_details? Did you narrow down the visleafs?

Yes. I made a lot of stuff as func details (and all that, as i said.)

Best way, is simply move bottom sky-wall to the side, make a little hole.

No, that is the worst way! Sorry, but if i understood what you meant, it seems like you are making a leak with purpose. Leaks are not good (eventhough they make compile time faster) 'coz the cause lag, texture problems ( especially on reflective textures), problems in models (again: especially in the reflective ones) etc.

Work fine for me

Anyway if it so bad. use it only for test map. Do not use it for final release. (Using that way takes me only 2 min to convert map instead 6hours .)