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

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

On 06/12/2018 08:35 AM, Tiwei Bie wrote:
> 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.


Thanks for the heads-up, I hadn't tried with virtio-user.
I'll post a new version with this fixed soon.

> 
>> 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[] = {

Yeah, I missed the warning when running my build scripts and noticed
it from the upstream CI mail.

It will be fixed in next version.

Thanks!
Maxime

> Best regards,
> Tiwei Bie
>