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

Chris Snook
2007-08-13T12:26:56Z

David Howells wrote:
> Chris Snook <csnook@redhat.com> 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