cvs commit: src/sys/alpha/alpha machdep.c src/sys/alpha/include cpuconf.h src/sys/alpha/pci lca.c lcareg.h

[Bernd Walter]

On Tue, Feb 01, 2005 at 11:32:13AM -0500, John Baldwin wrote:
> On Tuesday 01 February 2005 10:28 am, Bernd Walter wrote:
> > Would the PAL call work for SMP systems?
> 
> Yes, though it says that the CPU counter can slow down while it is in the 
> waiting state, so it seems that PAL is free to implement something just like 
> what you did.

I'm more worried about wakeup e.g. in case of one CPU releasing a lock
another is waiting for.

> > AFAIK no alpha CPU has native halt support so there is not much magic
> > that PAL can do for us.
> > What I've found out about this case is that alpha CPUs automaticaly
> > reduce power on unused parts and running just a tight loop, that works
> > without memory access, for a few microsecsonds might be more efficient
> > do do it ourself than calling PAL, which must be doing something
> > similar.
> > At least I think it is possible to reduce idle power consumption from
> > the current situation either way.
> 
> Yes, right now we buzz loop with a memory access on each iteration, we could 
> add a for loop that just decrements a counter to zero to the idle loop if 
> desired.  With preemption turned on we could have the idle process not check 
> the run queues at all and just sit in a buzz loop.

Exactly this is what I was thinking about, but wanted to do power
measurements first.
But my priority has more interessting stuff first - the lca code
already existed for years now.

-- 
B.Walter                   BWCT                http://www.bwct.de
bernd at bwct.de                                  info at bwct.de