From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH v2] vhost: Add indirect descriptors support
 to the TX path
Date: Fri, 23 Sep 2016 13:28:05 -0700
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Cc: Maxime Coquelin <maxime.coquelin@redhat.com>,
 yuanhan.liu@linux.intel.com, huawei.xie@intel.com, dev@dpdk.org,
 vkaplans@redhat.com
To: "Michael S. Tsirkin" <mst@redhat.com>
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On Fri, 23 Sep 2016 21:31:27 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Fri, Sep 23, 2016 at 11:24:16AM -0700, Stephen Hemminger wrote:
> > On Fri, 23 Sep 2016 09:16:49 +0200
> > Maxime Coquelin <maxime.coquelin@redhat.com> wrote:
> >   
> > > Indirect descriptors are usually supported by virtio-net devices,
> > > allowing to dispatch a larger number of requests.
> > > 
> > > When the virtio device sends a packet using indirect descriptors,
> > > only one slot is used in the ring, even for large packets.
> > > 
> > > The main effect is to improve the 0% packet loss benchmark.
> > > A PVP benchmark using Moongen (64 bytes) on the TE, and testpmd
> > > (fwd io for host, macswap for VM) on DUT shows a +50% gain for
> > > zero loss.
> > > 
> > > On the downside, micro-benchmark using testpmd txonly in VM and
> > > rxonly on host shows a loss between 1 and 4%.i But depending on
> > > the needs, feature can be disabled at VM boot time by passing
> > > indirect_desc=off argument to vhost-user device in Qemu.
> > > 
> > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>  
> > 
> > What about supporting VIRTIO_F_ANY_LAYOUT?  
> 
> I thought it's already supported.
> That's required by virtio 1 and dpdk claims support for that.
> 

I don't see the flag set in the DPDK vhost driver feature bits
(at least in the source). 

/* Features supported by this lib. */
#define VHOST_SUPPORTED_FEATURES ((1ULL << VIRTIO_NET_F_MRG_RXBUF) | \
				(1ULL << VIRTIO_NET_F_CTRL_VQ) | \
				(1ULL << VIRTIO_NET_F_CTRL_RX) | \
				(1ULL << VIRTIO_NET_F_GUEST_ANNOUNCE) | \
				(VHOST_SUPPORTS_MQ)            | \
				(1ULL << VIRTIO_F_VERSION_1)   | \
				(1ULL << VHOST_F_LOG_ALL)      | \
				(1ULL << VHOST_USER_F_PROTOCOL_FEATURES) | \
				(1ULL << VIRTIO_NET_F_HOST_TSO4) | \
				(1ULL << VIRTIO_NET_F_HOST_TSO6) | \
				(1ULL << VIRTIO_NET_F_CSUM)    | \
				(1ULL << VIRTIO_NET_F_GUEST_CSUM) | \
				(1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
				(1ULL << VIRTIO_NET_F_GUEST_TSO6))