Re: [PATCH] vhost: add back support for concurrent enqueue

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Mon, Aug 15, 2016 at 01:00:24PM -0700, Rich Lane wrote:
> Concurrent enqueue is an important performance optimization when the number
> of cores used for switching is different than the number of vhost queues.
> I've observed a 20% performance improvement compared to a strategy that
> binds queues to cores.
> 
> The atomic cmpset is only executed when the application calls
> rte_vhost_enqueue_burst_mp. Benchmarks show no performance impact
> when not using concurrent enqueue.
> 
> Mergeable RX buffers aren't supported by concurrent enqueue to minimize
> code complexity.

I think that would break things when Mergeable rx is enabled (which is
actually enabled by default).

Besides that, as mentioned in the last week f2f talk, do you think adding
a new flag RTE_VHOST_USER_CONCURRENT_ENQUEUE (for rte_vhost_driver_register())
__might__ be a better idea? That could save us a API, to which I don't object
though.

	--yliu