Re: [dpdk-dev] [PATCH] vhost: Clean iotlb cache on vring stop

["Xia, Chenbo" <chenbo.xia@intel.com>]

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Thursday, September 23, 2021 4:34 PM
> To: Eugenio Pérez <eperezma@redhat.com>; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Pei Zhang <pezhang@redhat.com>; Jason Wang
> <jasowang@redhat.com>
> Subject: Re: [PATCH] vhost: Clean iotlb cache on vring stop
> 
> 
> 
> On 8/27/21 18:12, Eugenio Pérez wrote:
> > Old IOVA cache entries are left when there is a change on virtio driver
> > in VM. In case that all these old entries have iova addresses lesser
> > than new iova entries, vhost code will need to iterate all the cache to
> > find the new ones. In case of just a new iova entry needed for the new
> > translations, this condition will last forever.
> >
> > This has been observed in virtio-net to testpmd's vfio-pci driver
> > transition, reducing the performance from more than 10Mpps to less than
> > 0.07Mpps if the hugepage address was higher than the networking
> > buffers. Since all new buffers are contained in this new gigantic page,
> > vhost needs to scan IOTLB_CACHE_SIZE - 1 for each translation at worst.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > Reported-by: Pei Zhang <pezhang@redhat.com>
> > ---
> >   lib/vhost/vhost_user.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> > index 29a4c9af60..7de48f5333 100644
> > --- a/lib/vhost/vhost_user.c
> > +++ b/lib/vhost/vhost_user.c
> > @@ -2113,6 +2113,8 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
> >   	msg->size = sizeof(msg->payload.state);
> >   	msg->fd_num = 0;
> >
> > +	vhost_user_iotlb_flush_all(vq);
> > +
> >   	vring_invalidate(dev, vq);
> >
> >   	return RTE_VHOST_MSG_RESULT_REPLY;
> >
> 
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

So you will fix title and add fix tag when applying, right?

/Chenbo

> 
> Thanks,
> Maxime