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

[Chris Snook]

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.
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