Re: [dpdk-dev] [PATCH v2] vhost: fix mbuf alloc failure

[Flavio Leitner <fbl@sysclose.org>]

On Mon, May 04, 2020 at 10:41:17PM +0530, Sivaprasad Tummala wrote:
> vhost buffer allocation is successful for packets that fit
> into a linear buffer. If it fails, vhost library is expected
> to drop the current packet and skip to the next.
> 
> The patch fixes the error scenario by skipping to next packet.
> Note: Drop counters are not currently supported.
> 
> Fixes: c3ff0ac70acb ("vhost: improve performance by supporting large buffer")
> Cc: stable@dpdk.org
> Cc: fbl@sysclose.org
> 
> ---
> v2:
>  * fixed review comments - Maxime Coquelin
>  * fixed mbuf alloc errors for packed virtqueues - Maxime Coquelin
>  * fixed mbuf copy errors - Flavio Leitner
> 
> Signed-off-by: Sivaprasad Tummala <Sivaprasad.Tummala@intel.com>
> ---
>  lib/librte_vhost/virtio_net.c | 50 ++++++++++++++++++++++++++---------
>  1 file changed, 37 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 1fc30c681..764c514fd 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -1674,6 +1674,7 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  {
>  	uint16_t i;
>  	uint16_t free_entries;
> +	uint16_t dropped = 0;
>  
>  	if (unlikely(dev->dequeue_zero_copy)) {
>  		struct zcopy_mbuf *zmbuf, *next;
> @@ -1737,13 +1738,31 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  			update_shadow_used_ring_split(vq, head_idx, 0);
>  
>  		pkts[i] = virtio_dev_pktmbuf_alloc(dev, mbuf_pool, buf_len);
> -		if (unlikely(pkts[i] == NULL))
> +		if (unlikely(pkts[i] == NULL)) {
> +			/*
> +			 * mbuf allocation fails for jumbo packets when external
> +			 * buffer allocation is not allowed and linear buffer
> +			 * is required. Drop this packet.
> +			 */
> +#ifdef RTE_LIBRTE_VHOST_DEBUG
> +			VHOST_LOG_DATA(ERR,
> +				"Failed to allocate memory for mbuf. Packet dropped!\n");
> +#endif

That message is useful to spot that missing packets that happens
once in a while, so we should be able to see it even in production
without debug enabled. However, we can't let it flood the log.

I am not sure if librte eal has this functionality, but if not you
could limit by using a static bool:

static bool allocerr_warned = false;

if (allocerr_warned) {
    VHOST_LOG_DATA(ERR,
    "Failed to allocate memory for mbuf. Packet dropped!\n");
    allocerr_warned = true;
}



> +			dropped += 1;
> +			i++;
>  			break;
> +		}
>  
>  		err = copy_desc_to_mbuf(dev, vq, buf_vec, nr_vec, pkts[i],
>  				mbuf_pool);
>  		if (unlikely(err)) {
>  			rte_pktmbuf_free(pkts[i]);
> +#ifdef RTE_LIBRTE_VHOST_DEBUG
> +			VHOST_LOG_DATA(ERR,
> +				"Failed to copy desc to mbuf. Packet dropped!\n");
> +#endif

Same here.


> +			dropped += 1;
> +			i++;
>  			break;
>  		}
>  
> @@ -1753,6 +1772,8 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  			zmbuf = get_zmbuf(vq);
>  			if (!zmbuf) {
>  				rte_pktmbuf_free(pkts[i]);
> +				dropped += 1;
> +				i++;
>  				break;
>  			}
>  			zmbuf->mbuf = pkts[i];
> @@ -1782,7 +1803,7 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  		}
>  	}
>  
> -	return i;
> +	return (i - dropped);
>  }
>  
>  static __rte_always_inline int
> @@ -1946,21 +1967,24 @@ virtio_dev_tx_single_packed(struct virtio_net *dev,
>  			    struct rte_mbuf **pkts)
>  {
>  
> -	uint16_t buf_id, desc_count;
> +	uint16_t buf_id, desc_count = 0;
> +	int ret;
>  
> -	if (vhost_dequeue_single_packed(dev, vq, mbuf_pool, pkts, &buf_id,
> -					&desc_count))
> -		return -1;
> +	ret = vhost_dequeue_single_packed(dev, vq, mbuf_pool, pkts, &buf_id,
> +					&desc_count);
>  
> -	if (virtio_net_is_inorder(dev))
> -		vhost_shadow_dequeue_single_packed_inorder(vq, buf_id,
> -							   desc_count);
> -	else
> -		vhost_shadow_dequeue_single_packed(vq, buf_id, desc_count);
> +	if (likely(desc_count > 0)) {


The vhost_dequeue_single_packed() could return -1 with desc_count > 0
and this change doesn't handle that.

Thanks,
fbl


> +		if (virtio_net_is_inorder(dev))
> +			vhost_shadow_dequeue_single_packed_inorder(vq, buf_id,
> +								   desc_count);
> +		else
> +			vhost_shadow_dequeue_single_packed(vq, buf_id,
> +					desc_count);
>  
> -	vq_inc_last_avail_packed(vq, desc_count);
> +		vq_inc_last_avail_packed(vq, desc_count);
> +	}
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static __rte_always_inline int
> -- 
> 2.17.1
> 

-- 
fbl