Re: [dpdk-dev] [PATCH] vhost: add vDPA resource cleanup callback

["Xueming(Steven) Li" <xuemingl@nvidia.com>]

On Wed, 2021-11-03 at 09:46 +0100, Maxime Coquelin wrote:
> 
> On 11/3/21 09:41, Xia, Chenbo wrote:
> > Hi Xueming,
> > 
> > > -----Original Message-----
> > > From: Xueming(Steven) Li <xuemingl@nvidia.com>
> > > Sent: Thursday, October 21, 2021 8:36 PM
> > > To: maxime.coquelin@redhat.com; dev@dpdk.org
> > > Cc: Xia, Chenbo <chenbo.xia@intel.com>
> > > Subject: Re: [PATCH] vhost: add vDPA resource cleanup callback
> > > 
> > > On Thu, 2021-10-21 at 14:00 +0200, Maxime Coquelin wrote:
> > > > Hi Xueming,
> > > > 
> > > > On 10/19/21 13:39, Xueming Li wrote:
> > > > > This patch adds vDPA device cleanup callback to release resources on
> > > > > vhost user connection close.
> > > > > 
> > > > > Signed-off-by: Xueming Li <xuemingl@nvidia.com>
> > > > > ---
> > > > >    lib/vhost/rte_vdpa_dev.h | 3 +++
> > > > >    lib/vhost/vhost_user.c   | 6 ++++++
> > > > >    2 files changed, 9 insertions(+)
> > > > > 
> > > > > diff --git a/lib/vhost/rte_vdpa_dev.h b/lib/vhost/rte_vdpa_dev.h
> > > > > index b0f494815fa..2711004fe05 100644
> > > > > --- a/lib/vhost/rte_vdpa_dev.h
> > > > > +++ b/lib/vhost/rte_vdpa_dev.h
> > > > > @@ -32,6 +32,9 @@ struct rte_vdpa_dev_ops {
> > > > >    	/** Driver close the device (Mandatory) */
> > > > >    	int (*dev_close)(int vid);
> > > > > 
> > > > > +	/** Connection closed, clean up resources */
> > > > > +	int (*dev_cleanup)(int vid);
> > > > > +
> > > > >    	/** Enable/disable this vring (Mandatory) */
> > > > >    	int (*set_vring_state)(int vid, int vring, int state);
> > > > > 
> > > > > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> > > > > index 5a894ca0cc7..032b621c86c 100644
> > > > > --- a/lib/vhost/vhost_user.c
> > > > > +++ b/lib/vhost/vhost_user.c
> > > > > @@ -162,6 +162,12 @@ free_mem_region(struct virtio_net *dev)
> > > > >    void
> > > > >    vhost_backend_cleanup(struct virtio_net *dev)
> > > > >    {
> > > > > +	struct rte_vdpa_device *vdpa_dev;
> > > > > +
> > > > > +	vdpa_dev = dev->vdpa_dev;
> > > > > +	if (vdpa_dev && vdpa_dev->ops->dev_cleanup != NULL)
> > > > > +		vdpa_dev->ops->dev_cleanup(dev->vid);
> > > > > +
> > > > >    	if (dev->mem) {
> > > > >    		free_mem_region(dev);
> > > > >    		rte_free(dev->mem);
> > > > > 
> > > > 
> > > > What will be done there that cannot be done in .dev_close()?
> > > 
> > > .dev_close() mainly handles VM suspend and driver reset. If release
> > > everything inside dev_close(), the suspend and resume takes longer time
> > > if number of VQs are huge. Customer want to upgrade VM configuration
> > > using suspend and resume, pause customer VM too long can't be accepted.
> > 
> > By saying 'upgrade VM configuration', do you mean VM memory hotplug? Or something
> > more?
> > 
> > Is this patch a next-step improvement of this commit?
> > 
> > commit 127f9c6f7b78a47b73b3e1c39e021cc81a30b4c9
> > Author: Matan Azrad <matan@mellanox.com>
> > Date:   Mon Jun 29 14:08:19 2020 +0000
> > 
> >      vhost: handle memory hotplug with vDPA devices
> > 
> >      Some vDPA drivers' basic configurations should be updated when the
> >      guest memory is hotplugged.
> > 
> >      Close vDPA device before hotplug operation and recreate it after the
> >      hotplug operation is done.
> > 
> >      Signed-off-by: Matan Azrad <matan@mellanox.com>
> >      Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >      Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>
> > 
> > > So the idea is to cache and reuse resource between dev_close() and
> > > dev_conf(). Actually, the two functions looks more like dev_stop() and
> > > dev_start().
> > > 
> > > dev_cleanup hooks to vhost backend cleanup which called when socket
> > > closed for both client and server mode, a safe point to cleanup all
> > > cached resources.
> > > 
> > > > Having the mlx5 implementation of this callback alongside this patch may
> > > > help to understand.
> > > 
> > > The mlx5 implementation still a prototype, pending on internal review.
> > > So I just post the vhost part to get suggestion/comment. Let me know if
> > > the ugly code does help :)
> > 
> > I would prefer to see the mlx implementation with this patch in the same
> > patchset to understand the problem. A new callback is fine if the problem
> > itself makes sense :)
> 
> FYI, I'm about to apply a patch that marks the vDPA driver API as
> internal, when you will submit a new version please apply on top of it.

Haven't check your patch yet, but sounds good form subject :)

> 
> Thanks,
> Maxime
> 
> > Thanks,
> > Chenbo
> > 
> > > 
> > > > 
> > > > Thanks,
> > > > Maxime
> > > > 
> > 
>