Re: geom_sched usage

On Monday 18 October 2010 21:51:25 Luigi Rizzo wrote:
> On Mon, Oct 18, 2010 at 09:43:28AM +0200, David Naylor wrote:
> > Hi,
> > 
> > I've used geom_sched to some success.  Normally I do not notice anything
> > but today I was copying big files over a gigabit ethernet and my laptop
> > was not very responsive.  I loaded gsched and the responsiveness
> > improved (although still rather bad for anything requiring something
> > from the HDD).
> > 
> > Thank you for all this work :-)
> > 
> > Some questions I have:
> >  - with a gmirror should the gsched be attached to the underlying devices
> >  (aka
> > 
> > /dev/ad?) or to the mirror device (aka /dev/mirror/?)?
> 
> always attach as close as possible to the hardware.

Thanks.  

> >  - is there anyway to automatically attach gsched to a device on startup
> >  (i.e.
> > 
> > in rc.conf)?
> 
> no, you have to build some script yourself.

Would there be any interest in having a rc.d/ script?  I would find it 
conveniant to specify a single rc.conf line and get scheduling for all my 
devices.  PC-BSD might find such functionality useful.  

See attached for my first draft at such a script, I'm willing to hash it into 
shape.  

> >  - is there a way to prioritise random IO (vs sequential reads from big
> > 
> > files)?
> 
> no way to do that, but you can modify the quantum size and time to
> let sequential reads get shorter chunks
> 
> kern.geom.sched.rr.quantum_kb: 8192
> kern.geom.sched.rr.quantum_ms: 100
> kern.geom.sched.rr.wait_ms: 10
> 
> e.g. on a laptop it might make sense to set
> quantum_ms=50 and quantum_kb=2048

Is there a manual page that describes these sysctls?  It looks like, in my 
case, scp just hogs resources.  

I do perceive some improvements in normal usage.  Thanks

> >  - gsched_as does not appear to be installed.
> 
> true, gsched_as was just a proof of concept and gsched_rr
> includes anticipation and round robin, so it is a superset of gsched_as

Thanks for clarity.

Regards,

David