Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv

From: Chris Snook <[email-masked]>
Date: Mon, 13 Aug 2007 02:44:13 -0400

David Howells wrote:
> Chris Snook <[email-masked]> wrote:
> 
>> cpu_relax() contains a barrier, so it should do the right thing.  For non-smp
>> architectures, I'm concerned about interacting with interrupt handlers.  Some
>> drivers do use atomic_* operations.
> 
> I'm not sure that actually answers my question.  Why not smp_rmb()?
> 
> David

I would assume because we want to waste time efficiently even on non-smp 
architectures, rather than frying the CPU or draining the battery.  Certain 
looping execution patterns can cause the CPU to operate above thermal design 
power.  I have fans on my workstation that only ever come on when running 
LINPACK, and that's generally memory bandwidth-bound.  Just imagine what happens 
when you're executing the same few non-serializing instructions in a tight loop 
without ever stalling on memory fetches, or being scheduled out.

If there's another reason, I'd like to hear it too, because I'm just guessing here.

	-- Chris