From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Wang, Zhihong" <zhihong.wang@intel.com>
Subject: Re: [PATCH v5 2/6] vhost: rewrite enqueue
Date: Wed, 14 Sep 2016 08:22:39 +0000
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> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Tuesday, September 13, 2016 12:27 AM
> To: Wang, Zhihong <zhihong.wang@intel.com>; dev@dpdk.org
> Cc: yuanhan.liu@linux.intel.com; thomas.monjalon@6wind.com
> Subject: Re: [PATCH v5 2/6] vhost: rewrite enqueue
>=20
>=20
>=20
> On 09/09/2016 05:39 AM, Zhihong Wang wrote:
> >
> > +static inline void __attribute__((always_inline))
> > +notify_guest(struct virtio_net *dev, struct vhost_virtqueue *vq)
> > +{
> >  	rte_smp_wmb();
> > -
> > -	*(volatile uint16_t *)&vq->used->idx +=3D count;
> > -	vq->last_used_idx +=3D count;
> > -	vhost_log_used_vring(dev, vq,
> > -		offsetof(struct vring_used, idx),
> > -		sizeof(vq->used->idx));
> > -
> > -	/* flush used->idx update before we read avail->flags. */
> Please don't remove comments if not justified.
> Here the comment is important, as it explains why the barrier is needed.

Okay.

> > +	*(volatile uint16_t *)&vq->used->idx =3D vq->last_used_idx;
> > +	vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
> > +			sizeof(vq->used->idx));
> >  	rte_mb();
> > -
> > -	/* Kick the guest if necessary. */
> >  	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> >  			&& (vq->callfd >=3D 0))
> >  		eventfd_write(vq->callfd, (eventfd_t)1);
> > -	return count;
> >  }