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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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.


> 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
>