Re: performance loss on real time linux

[Pierangelo Masarati <ando@sys-net.it>]

Michael Ströder wrote:
> Pierangelo Masarati wrote:
>   
> > run a simple test using OpenLDAP 2.3.28 running on Linux 2.6.17 with
> > RTAI, compared to the stock 2.3.6.15 kernel f the distribution
> >     
>                               ^^^^^^^^
> Do you mean stock 2.6.15?
>   
No, I have no idea.
>   
> > - searching for the same entry, after it's in cache, requires ~0.008s w/
> > RTAI, and ~0.080s w/o RTAI (ten times longer!  It's a slightly different
> > kernel, but running on exactly the same machine, [..]
> >     
>
> Are you sure there haven't been any significant changes to the scheduler
> between these two kernel versions anyway? Also distributions most times
> ship with a patched kernel. So exact comparison should be done with a
> vanilla kernel and the very same kernel with RTAI.
>   
I concur.  The point is that to apply RTAI patch we need an official 
kernel release (usually the latest, or occasionally the latest-but-one), 
but usually we only rebuild it with the RTAI patch, and not without 
(there's no need to).  So, just to have an idea of how OpenLDAP behaved 
with the RT scheduling, I simply ran the same tests with the 
distribution's kernel.  The distribution was Ubuntu, but I don't 
remember the version or any other detail.  Only in case of dramatically 
slower response I would have checked more carefully those details.

p.