Re: [PATCH] "volatile considered harmful", take 3

["H. Peter Anvin" <hpa@zytor.com>]

Satyam Sharma wrote:
> 
>> +  - Pointers to data structures in coherent memory which might be
>> modified
>> +    by I/O devices can, sometimes, legitimately be volatile.  A ring
>> buffer
>> +    used by a network adapter, where that adapter changes pointers to
>> +    indicate which descriptors have been processed, is an example of
>> this
>> +    type of situation.
> 
> is a legitimate use case for volatile is still not clear to me (I
> agree with Alan's
> comment in a previous thread that this seems to be a case where a memory
> barrier would be applicable^Wbetter, actually). I could be wrong here, so
> would be nice if Peter explains why volatile is legitimate here.
> 
> Otherwise, it's fine with me.
> 

I don't see why Alan's way is necessarily better; it should work but is
more heavy-handed as it's disabling *all* optimization such as loop
invariants across the barrier.

	-hpa