[dpdk-dev] [PATCH] vhost: add back support for concurrent enqueue

[Rich Lane]

On Mon, Aug 22, 2016 at 7:16 AM, Yuanhan Liu <yuanhan.liu at linux.intel.com>
wrote:

> 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
>

Yes, I'd noticed that these patches would conflict. Once the vhost-cuse
removal and
Zhihong's patches have merged I'll send a new version.