AD DC LDAP server multi-process - slower!

[Jeremy Allison]

On Tue, Dec 13, 2016 at 04:43:19PM +1300, Andrew Bartlett wrote:
> G'Day,
> 
> We had a simple patch to change the single process LDAP server into
> multi-process, in the standard model like smbd uses, one fork per
> connection. 
> 
> The performance on a test of 
>  - connect
>  - NTLM binds
>  - drop socket
> showed using multiple processes this way, with the high exit cost, is
> actually slower.  We expected that having mutiple CPUs available would
> make it at least a little faster, and we would optimise from there with
> the talloc_for_exit() or similar.
> 
> We will re-investigate the prefork process model for the ldap server. 

Yes, interestingly enough Volker predicted that to me in a phone
call due to the case below.

Are you sure this is the exit cost ? When we have many shared
libraries the cost of setting up the vm mappings on fork can also
be very expensive.