Re: [dpdk-dev] [PATCH] net/virtio: fix indirect descriptors reconnection

["Ding, Xuan" <xuan.ding@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Thursday, September 23, 2021 4:16 PM
> To: Ding, Xuan <xuan.ding@intel.com>; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Wang, Yinan
> <yinan.wang@intel.com>; stable@dpdk.org; Liu, Yong <yong.liu@intel.com>
> Subject: Re: [PATCH] net/virtio: fix indirect descriptors reconnection
> 
> Hi Xuan,
> 
> On 8/19/21 07:35, Xuan Ding wrote:
> > Since packed indirect descriptors are added and initialized when
> > initializing vring, the reconnection path also needs to be considered.
> >
> > Fixes: 381f39ebb78a ("net/virtio: fix packed ring indirect descricptors setup")
> > Cc: stable@dpdk.org
> > Cc: yong.liu@intel.com
> >
> > Signed-off-by: Xuan Ding <xuan.ding@intel.com>
> > ---
> >   drivers/net/virtio/virtqueue.c | 14 ++++++++++++++
> >   1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/net/virtio/virtqueue.c b/drivers/net/virtio/virtqueue.c
> > index 1f9af3c31b..47229f35c4 100644
> > --- a/drivers/net/virtio/virtqueue.c
> > +++ b/drivers/net/virtio/virtqueue.c
> > @@ -208,6 +208,20 @@ virtqueue_txvq_reset_packed(struct virtqueue *vq)
> >   			rte_pktmbuf_free(dxp->cookie);
> >   			dxp->cookie = NULL;
> >   		}
> 
> It makes me think we might save quite some bytes by not allocating
> indirect descriptors when feature is not negotiated, but it might have
> a cost in term of performance.

Do you mean we allocate the indirect descriptors after checking the indirect feature in virtio TX queue,
instead of allocating it at initialization?
If so, that makes sense, and hence we don't to initialize it in two places.

> 
> > +
> > +		struct virtio_tx_region *txr;
> 
> Don't mix declarations within code.
> 
> > +		txr = txvq->virtio_net_hdr_mz->addr;
> > +		/* first indirect descriptor is always the tx header */
> > +		struct vring_packed_desc *start_dp =
> > +			txr[desc_idx].tx_packed_indir;
> 
> Ditto.

Thanks, will update in next version.

Regards,
Xuan

> 
> > +		vring_desc_init_indirect_packed(start_dp,
> > +		      RTE_DIM(txr[desc_idx].tx_packed_indir));
> > +		start_dp->addr = txvq->virtio_net_hdr_mem
> > +			+ desc_idx * sizeof(*txr)
> > +			+ offsetof(struct virtio_tx_region,
> > +				   tx_hdr);
> > +		start_dp->len = vq->hw->vtnet_hdr_size;
> > +
> >   	}
> >
> >   	vring_desc_init_packed(vq, size);
> >
> 
> Thanks,
> Maxime