[PATCH 00/16] big.LITTLE low-level CPU and cluster power management

[pavel@ucw.cz (Pavel Machek)]

Hi!

> > > > I'd say:
> > > > 
> > > > * expose all 8 cores.
> > > 
> > > You may do that now.  However the resulting power efficiency is far from 
> > > optimal.
> > 
> > Really? Assuming the lwn article is accurate, it will be exactly the
> > same.
> > 
> > I propose exposing all 8 cores, then keeping 4 of them offline in
> > normal operation. This should have characteristics of your solution,
> > except that cpu does not change unexpectedly under the pinned tasks.
> > 
> > > > * as long as scheduler is not ready, you can offline "the other" set of cores...
> > > > 	/sys/.../cpu/..../online
> > > 
> > > You may do that now also.  But system performance is far from optimal.
> > 
> > Really? Do the offlining from the cpufreq code, and solution will be
> > equivalent to yours, except the hacks.
> 
> No it is not equivalent.  Offlining a CPU is a fairly heavy operation in 
> Linux and you don't want to do that multiple times per second for 
> example.  Whereas the switcher "hack" is similar to a context switch in 
> terms of software complexity.

Well, why not. Logically, you _are_ saving state, offlining, onlining,
and restoring state, multiple times per second, already. Fast
offline/online benefits everyone... 

As for the hacks... what does /proc/cpuinfo show on your system? What
happens when process requests binding to specific cpu? I fear that
switching hack is easy now, but will have unnice impact on unexpected
places.

BTW I guess this should be discussed on linux-kernel, not on the arm
list.
									Pavel
-- 
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