Re: [PATCH 1/24] make atomic_read() behave consistently on alpha

[Chris Snook <csnook@redhat.com>]

Segher Boessenkool wrote:
>>> The only safe way to get atomic accesses is to write
>>> assembler code.  Are there any downsides to that?  I don't
>>> see any.
>>
>> The assumption that aligned word reads and writes are atomic, and that 
>> words are aligned unless explicitly packed otherwise, is endemic in 
>> the kernel.  No sane compiler violates this assumption.  It's true 
>> that we're not portable to insane compilers after this patch, but we 
>> never were in the first place.
> 
> You didn't answer my question: are there any downsides to using
> explicit coded-in-assembler accesses for atomic accesses?  You
> can handwave all you want that it should "just work" with
> volatile accesses, but volatility != atomicity, volatile in C
> is really badly defined, GCC never officially gave stronger
> guarantees, and we have a bugzilla full of PRs to show what a
> minefield it is.
> 
> So, why not use the well-defined alternative?

Because we don't need to, and it hurts performance.