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Subject: RE: Re: time to sleep?
From: Nielsen Linus (ext) (Linus.Nielsen_at_elema.siemens.se)
Date: 2002-08-23


> So, I'm all for using sleep modes. However, if you are really going to
> reduce power then you should sleep as much as possible. And
> you cannot do that if you are using inefficient code.

My point exactly. However, as you put it (or rather, how i interpreted your
text) you seemed to think that the memory accesses themselves added to the
power consumtion even without a sleep mode.

> Now, code that usually is not considered inefficient can be
> very inefficient if you look at the power usage. I gave some
> pointers to what I believe are good programming standards.

I'm sure that you know a lot more than I do in this matter. Then please
explain how the power consumption can be lowered by keeping the variables in
registers, when the RAM is accessed for every instruction anyway.

<large cache functionality description removed>

> What is, however, commonly agreed upon as a good thing as to
> save power is using compiler optimizations to make short
> efficient code with few memory references and writing
> efficient code.

Yes, it is always a good thing to write efficient code. What I objected to
was that you wrote that efficient code in itself will draw less power. I say
that it won't unless the CPU sleeps when it is done.

It is self-evident that the optimized code will save power because the CPU
can go to sleep sooner-

> You mention that the SH is a RISC. I should perhaps mention
> that IMO "RISC" doesn't really mean anything. The SH is a load-store
> architecture and that is much more important.

True.

> To me it looks like you believe I'm against using sleep mode.
> I'm not, never was, and I frankly cannot see how you could
> deduce that.

I thought so, since you only talked about optimizing the code and nothing
about the sleep.

> I'm not looking for a fight. I do tend to be bit agitated,
> though, when people are using arguments that I don't believe
> are true.

Please point out what was untrue in my arguments, so i can learn something
for my next "fight". :-)

/Linus



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