On Thu, Aug 18, 2016 at 11:27:06AM -0700, Rich Lane wrote:
> On Mon, Aug 15, 2016 at 7:37 PM, Yuanhan Liu <yuanhan.liu at linux.intel.com>
> wrote:
>
> 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).
>
>
> Would it be reasonable to return -ENOTSUP in this case, and restrict
> concurrent
> enqueue
> to devices where VIRTIO_NET_F_MRG_RXBUF is disabled?
>
> I could also add back concurrent enqueue support for mergeable RX, but I was
> hoping to avoid
> that since the mergeable codepath is already complex and wouldn't be used in
> high performance
> deployments.
Another note is that, you might also have noticed, Zhihong made a patch
set [0] to optimize the enqueue code path (mainly on mergeable path). It
basically does a rewrite from scatch, which removes the desc buf reservation,
meaning it would be harder to do concurrent enqueue support based on that.
[0]: Aug 19 Zhihong Wang ( 68) ??>[PATCH v3 0/5] vhost: optimize enqueue
--yliu
