From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Paul Mackerras <paulus@samba.org>
Cc: LinuxPPC-dev <linuxppc-dev@ozlabs.org>
Subject: Re: CPU off power consumption
Date: Mon, 28 Nov 2005 13:52:48 +1100 [thread overview]
Message-ID: <1133146369.7768.170.camel@gaston> (raw)
In-Reply-To: <17290.26688.710369.613144@cargo.ozlabs.ibm.com>
On Mon, 2005-11-28 at 13:15 +1100, Paul Mackerras wrote:
> Giuliano Pochini writes:
>
> > Out of curiosity, what's the difference between a cpu that has never been
> > enabled and one that has been disabled with echo 0>/sys/.../online ? It
> > happens that when I boot with maxcpus=0 the temperature always stays low
> > enoung that the fan never spins up. If I enable and then I immediately
> > disable the 2nd cpu, the temperature goes a few degrees up. I have a dual
> > G4-MDD.
>
> Interesting. A cpu that has been disabled will be in sleep mode with
> interrupts disabled and its caches flushed. One that has never been
> started may possibly be held in the reset state. The way to check
> would be to check the state of the GPIO register that controls the
> soft reset line of the second CPU.
No, I think CPUs that have not been started are held in a similar sleep
loop in ROM. I don't see right away why there would be any power
consumption difference unless some bug causing us to never actually call
the sleep loop ....
Ben.
next prev parent reply other threads:[~2005-11-28 2:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-26 11:38 CPU off power consumption Giuliano Pochini
2005-11-28 2:15 ` Paul Mackerras
2005-11-28 2:52 ` Benjamin Herrenschmidt [this message]
2005-12-02 15:06 ` Giuliano Pochini
2005-12-05 3:59 ` Paul Mackerras
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