[dpdk-dev] [PATCH 2/5] ethdev: add port ownership

[Bruce Richardson]

On Tue, Dec 05, 2017 at 12:53:36PM +0100, Thomas Monjalon wrote:
> 05/12/2017 12:44, Ananyev, Konstantin:
> > Just forgot to mention - I don' think it is good idea to disallow secondary process to set  theowner.
> 
> I think we all agree on that.
> My initial suggestion was to use the ownership in secondary processes.
> I think Matan forbid it as a first step because there is no
> multi-process synchronization currently.
> 
> > Let say  in secondary process I have few tap/ring/pcap devices.
> > Why it shouldn't be allowed to unite them under bonding device and make that device to own them?
> > That's why I think get/set owner better to be atomic.
> > If the owner is just a pointer - in that case get operation will be atomic by nature,
> > set could be implemented just by CAS.
> 
> It would be perfect.
> Can we be sure that the atomic will work perfectly on shared memory?

The sharing of memory is an OS-level construct in managing page tables,
more than anything else. For atomic operations, a memory address is a
memory address, whether it is shared or private to a process.

> On every architectures?

All architectures should have an atomic compare-and-set equivalent
operation for it's native pointer size. In the unlikely case we have to
support one that doesn't, we can special-case that in some other way.