Re: [Ksummit-discuss] [TECH TOPIC] Memory model, using ISO C++11 atomic ops

[Hannes Reinecke <hare@suse.com>]

On 07/25/2016 07:14 PM, Luis R. Rodriguez wrote:
> On Fri, Jul 22, 2016 at 09:44:11AM -0700, Paul E. McKenney wrote:
>> On Fri, Jul 22, 2016 at 11:34:35AM +0100, David Howells wrote:
>>> Earlier this year we had a discussion of the possibilities of using ISO C++11
>>> atomic operations inside the kernel to implement kernel atomic ops of sorts
>>> various, posted here:
>>>
>>> 	Subject: [RFC PATCH 00/15] Provide atomics and bitops implemented with ISO C++11 atomics
>>> 	Date: Wed, 18 May 2016 16:10:37 +0100
>>>
>>> Is it worth getting together to discuss these in person in one of the tech
>>> slots - especially if there are some gcc or llvm people available at plumbers
>>> who could join in?
>>>
>>>
>>> Further, Paul McKenney and others are assembling a memory model description.
>>
>> We are attempting to automate memory-barriers.txt, so that you could
>> provide fragments of C code, and the tool would tell you whether a given
>> outcome happens always, sometimes, or never.  The current prototype
>> handles memory accesses, memory barriers, and RCU, but not yet locking
>> or read-modify-write atomics (though there is some vestigal support for
>> RMW atomics).  We are currently playing whack-a-mole with odd corner cases
>> of various architectures' memory models.  We are therefore also working
>> on ways of handling the resulting uncertainty.  Good clean fun!  ;-)
>
> Consider me interested in this discussion, patches, etc.
>
Same here.
I have been playing around with RCUs and memory barriers quite a lot 
recently, and found some really 'odd' use-cases in the kernel which 
would benefit from improvements here.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.com			               +49 911 74053 688
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