Re: [RFC/PATCH 0/3] sched: allow arch override of cpu power

[Nathan Lynch <ntl@pobox.com>]

Ingo Molnar wrote:
> 
> * Nathan Lynch <ntl@pobox.com> wrote:
> > So it would be nice to have the scheduler slightly prefer primary 
> > threads on POWER6 machines.  These patches, which allow the 
> > architecture to override the scheduler's CPU "power" calculation, are 
> > one possible approach, but I'm open to others.  Please note: these 
> > seemed to have the desired effect on 2.6.25-rc kernels (2-3% 
> > improvement in a kernbench-like make -j <nr_cores>), but I'm not 
> > seeing this improvement with 2.6.26-rc kernels for some reason I am 
> > still trying to track down.
> 
> ok, i guess that discrepancy has to be tracked down before we can think 
> about these patches - but the principle is OK.

Great.  I'll keep trying to figure out what's going on there.


> One problem is that the whole cpu-power balancing code in sched.c is a 
> bit ... unclear and under-documented. So any change to this area should 
> begin at documenting the basics: what do the units mean exactly, how are 
> they used in balancing and what is the desired effect.
>
> I'd not be surprised if there were a few buglets in this area, SMT is 
> not at the forefront of testing at the moment. There's nothing 
> spectacularly broken in it (i have a HT machine myself), but the 
> concepts have bitrotten a bit. Patches - even if they just add comments 
> - are welcome :-)

Okay, I'll have a look.  Thanks Ingo.