[dpdk-stable] [PATCH v4 2/2] ring: move the atomic load of head above the loop

[Honnappa Nagarahalli]

<Fixing this to make the reply inline, making email plain text>

 
On Thu, 1 Nov 2018 17:53:51 +0800 
Gavin Hu <mailto:gavin.hu at arm.com> wrote: 

> +* **Updated the ring library with C11 memory model.** 
> + 
> + Updated the ring library with C11 memory model including the following changes: 
> + 
> + * Synchronize the load and store of the tail 
> + * Move the atomic load of head above the loop 
> + 

Does this really need to be in the release notes? Is it a user visible change 
or just an internal/optimization and fix. 

[Gavin] There is no api changes, but this is a significant change as ring is fundamental and widely used, it decreases latency by 25% in our tests, it may do even better for cases with more contending producers/consumers or deeper depth of rings.

[Honnappa] I agree with Stephen. Release notes should be written from DPDK user perspective. In the rte_ring case, the user has the option of choosing between c11 and non-c11 algorithms. Performance would be one of the criteria to choose between these 2 algorithms. IMO, it probably makes sense to indicate that the performance of c11 based algorithm has been improved. However, I do not know what DPDK has followed historically regarding performance optimizations. I would prefer to follow whatever has been followed so far.
I do not think that we need to document the details of the internal changes since it does not help the user make a decision.