Re: [RFC][PATCH 0/5] arch: atomic rework

[Jeff Law <law@redhat.com>]

On 02/25/14 17:15, Paul E. McKenney wrote:
>> I have for the last several years been 100% convinced that the Intel
>> memory ordering is the right thing, and that people who like weak
>> memory ordering are wrong and should try to avoid reproducing if at
>> all possible. But given that we have memory orderings like power and
>> ARM, I don't actually see a sane way to get a good strong ordering.
>> You can teach compilers about cases like the above when they actually
>> see all the code and they could poison the value chain etc. But it
>> would be fairly painful, and once you cross object files (or even just
>> functions in the same compilation unit, for that matter), it goes from
>> painful to just "ridiculously not worth it".
>
> And I have indeed seen a post or two from you favoring stronger memory
> ordering over the past few years.  ;-)
I couldn't agree more.

>
> Are ARM and Power really the bad boys here?  Or are they instead playing
> the role of the canary in the coal mine?
That's a question I've been struggling with recently as well.  I suspect 
they (arm, power) are going to be the outliers rather than the canary. 
While the weaker model may give them some advantages WRT scalability, I 
don't think it'll ultimately be enough to overcome the difficulty in 
writing correct low level code for them.

Regardless, they're here and we have to deal with them.


Jeff