Re: [PATCH v3 1/5] net/virtio: forbid simple Tx path by default

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, Jun 07, 2018 at 11:26:12AM +0200, Maxime Coquelin wrote:
> Simple Tx path is not compliant with the Virtio specification,
> as it assumes the device will use the descriptors in order.
> 
> VIRTIO_F_IN_ORDER feature has been introduced recently, but the
> simple Tx path is not compliant with it as VIRTIO_F_IN_ORDER
> requires that chained descriptors are used sequentially, which
> is not the case in simple Tx path.
> 
> This patch introduces 'simple_tx_support' devarg to unlock
> Tx simple path selection.
> 
> Reported-by: Tiwei Bie <tiwei.bie@intel.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  doc/guides/nics/virtio.rst         |  9 +++++
>  drivers/net/virtio/virtio_ethdev.c | 73 +++++++++++++++++++++++++++++++++++++-
>  drivers/net/virtio/virtio_pci.h    |  1 +
>  3 files changed, 82 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst
> index 8922f9c0b..53ce1c12a 100644
> --- a/doc/guides/nics/virtio.rst
> +++ b/doc/guides/nics/virtio.rst
> @@ -222,6 +222,9 @@ Tx callbacks:
>  
>  #. ``virtio_xmit_pkts_simple``:
>     Vector version fixes the available ring indexes to optimize performance.
> +   This implementation does not comply with the Virtio specification, and so
> +   is not selectable by default. "simple_tx_support=1" devarg must be passed
> +   to unlock it.
>  
>  
>  By default, the non-vector callbacks are used:
> @@ -331,3 +334,9 @@ The user can specify below argument in devargs.
>      driver, and works as a HW vhost backend. This argument is used to specify
>      a virtio device needs to work in vDPA mode.
>      (Default: 0 (disabled))
> +
> +#.  ``simple_tx_support``:
> +
> +    This argument enables support for the simple Tx path, which is not
> +    compliant with the Virtio specification.
> +    (Default: 0 (disabled))

I tried this patch on my server. Virtio-user will
fail to probe when simple_tx_support is specified
dues to the check in virtio_user_pmd_probe():

PMD: Error parsing device, invalid key <simple_tx_support>
virtio_user_pmd_probe(): error when parsing param
vdev_probe(): failed to initialize virtio_user0 device
EAL: Bus (vdev) probe failed.


> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> index 5833dad73..052dd056a 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -1331,6 +1331,8 @@ set_rxtx_funcs(struct rte_eth_dev *eth_dev)
>  	if (hw->use_simple_tx) {
>  		PMD_INIT_LOG(INFO, "virtio: using simple Tx path on port %u",
>  			eth_dev->data->port_id);
> +		PMD_INIT_LOG(WARNING,
> +				"virtio: simple Tx path does not comply with Virtio spec");
>  		eth_dev->tx_pkt_burst = virtio_xmit_pkts_simple;
>  	} else {
>  		PMD_INIT_LOG(INFO, "virtio: using standard Tx path on port %u",
> @@ -1790,6 +1792,66 @@ rte_virtio_pmd_init(void)
>  	rte_pci_register(&rte_virtio_pmd);
>  }
>  
> +#define VIRTIO_SIMPLE_TX_SUPPORT "simple_tx_support"
> +
> +static int virtio_dev_args_check(const char *key, const char *val,
> +		void *opaque)
> +{
> +	struct rte_eth_dev *dev = opaque;
> +	struct virtio_hw *hw = dev->data->dev_private;
> +	unsigned long tmp;
> +	int ret = 0;
> +
> +	errno = 0;
> +	tmp = strtoul(val, NULL, 0);
> +	if (errno) {
> +		PMD_INIT_LOG(INFO,
> +				"%s: \"%s\" is not a valid integer", key, val);
> +		return errno;
> +	}
> +
> +	if (strcmp(VIRTIO_SIMPLE_TX_SUPPORT, key) == 0)
> +		hw->support_simple_tx = !!tmp;
> +
> +	return ret;
> +}
> +
> +static int
> +virtio_dev_args(struct rte_eth_dev *dev)
> +{
> +	struct rte_kvargs *kvlist;
> +	struct rte_devargs *devargs;
> +	const char *valid_args[] = {
> +		VIRTIO_SIMPLE_TX_SUPPORT,
> +		NULL,
> +	};

checkpatch is complaining about above definition:

WARNING:STATIC_CONST_CHAR_ARRAY: char * array declaration might be
better as static const
#96: FILE: drivers/net/virtio/virtio_ethdev.c:1824:
+       const char *valid_args[] = {

Best regards,
Tiwei Bie