Re: [dpdk-dev] [PATCH v4 4/7] vhost: fix NUMA reallocation with multiqueue

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

Hi Maxime,

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Friday, June 18, 2021 4:01 PM
> To: Xia, Chenbo <chenbo.xia@intel.com>; dev@dpdk.org;
> david.marchand@redhat.com
> Cc: stable@dpdk.org
> Subject: Re: [PATCH v4 4/7] vhost: fix NUMA reallocation with multiqueue
> 
> 
> 
> On 6/18/21 6:34 AM, Xia, Chenbo wrote:
> > Hi Maxime,
> >
> >> -----Original Message-----
> >> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> Sent: Thursday, June 17, 2021 11:38 PM
> >> To: dev@dpdk.org; david.marchand@redhat.com; Xia, Chenbo
> <chenbo.xia@intel.com>
> >> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; stable@dpdk.org
> >> Subject: [PATCH v4 4/7] vhost: fix NUMA reallocation with multiqueue
> >>
> >> Since the Vhost-user device initialization has been reworked,
> >> enabling the application to start using the device as soon as
> >> the first queue pair is ready, NUMA reallocation no more
> >> happened on queue pairs other than the first one since
> >> numa_realloc() was returning early if the device was running.
> >>
> >> This patch fixes this issue by only preventing the device
> >> metadata to be allocated if the device is running. For the
> >> virtqueues, a vring state change notification is sent to
> >> notify the application of its disablement. Since the callback
> >> is supposed to be blocking, it is safe to reallocate it
> >> afterwards.
> >
> > Is there a corner case? Numa_realloc may happen during vhost-user msg
> > set_vring_addr/kick, set_mem_table and iotlb msg. And iotlb msg will
> > not take vq access lock. It could happen when numa_realloc happens on
> > iotlb msg and app accesses vq in the meantime?
> 
> I think we are safe wrt to numa_realloc(), because the app's
> .vring_state_changed() callback is only returning when it is no more
> processing the rings.

Yes, I think it should be. But in this iotlb msg case (take vhost pmd for example),
can't vhost pmd still access vq since vq access lock is not took? Do I miss something?

Thanks,
Chenbo

> 
> 
> > Thanks,
> > Chenbo
> >
> >>
> >> Fixes: d0fcc38f5fa4 ("vhost: improve device readiness notifications")
> >> Cc: stable@dpdk.org
> >>
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> ---
> >>  lib/vhost/vhost_user.c | 11 ++++++++---
> >>  1 file changed, 8 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> >> index 0e9e26ebe0..6e7b327ef8 100644
> >> --- a/lib/vhost/vhost_user.c
> >> +++ b/lib/vhost/vhost_user.c
> >> @@ -488,9 +488,6 @@ numa_realloc(struct virtio_net *dev, int index)
> >>  	struct batch_copy_elem *new_batch_copy_elems;
> >>  	int ret;
> >>
> >> -	if (dev->flags & VIRTIO_DEV_RUNNING)
> >> -		return dev;
> >> -
> >>  	old_dev = dev;
> >>  	vq = old_vq = dev->virtqueue[index];
> >>
> >> @@ -506,6 +503,11 @@ numa_realloc(struct virtio_net *dev, int index)
> >>  		return dev;
> >>  	}
> >>  	if (oldnode != newnode) {
> >> +		if (vq->ready) {
> >> +			vq->ready = false;
> >> +			vhost_user_notify_queue_state(dev, index, 0);
> >> +		}
> >> +
> >>  		VHOST_LOG_CONFIG(INFO,
> >>  			"reallocate vq from %d to %d node\n", oldnode, newnode);
> >>  		vq = rte_malloc_socket(NULL, sizeof(*vq), 0, newnode);
> >> @@ -558,6 +560,9 @@ numa_realloc(struct virtio_net *dev, int index)
> >>  		rte_free(old_vq);
> >>  	}
> >>
> >> +	if (dev->flags & VIRTIO_DEV_RUNNING)
> >> +		goto out;
> >> +
> >>  	/* check if we need to reallocate dev */
> >>  	ret = get_mempolicy(&oldnode, NULL, 0, old_dev,
> >>  			    MPOL_F_NODE | MPOL_F_ADDR);
> >> --
> >> 2.31.1
> >