[dpdk-dev] [PATCH v2 03/12] virtio: reinitialize the device in configure callback

[Olivier MATZ]

Hello Yuanhan,

On 10/12/2016 04:41 PM, Yuanhan Liu wrote:
> On Mon, Oct 03, 2016 at 11:00:14AM +0200, Olivier Matz wrote:
>> @@ -1344,6 +1347,7 @@ virtio_dev_configure(struct rte_eth_dev *dev)
>>   {
>>   	const struct rte_eth_rxmode *rxmode = &dev->data->dev_conf.rxmode;
>>   	struct virtio_hw *hw = dev->data->dev_private;
>> +	uint64_t req_features;
>>   	int ret;
>>
>>   	PMD_INIT_LOG(DEBUG, "configure");
>> @@ -1353,6 +1357,14 @@ virtio_dev_configure(struct rte_eth_dev *dev)
>>   		return -EINVAL;
>>   	}
>>
>> +	req_features = VIRTIO_PMD_GUEST_FEATURES;
>> +	/* if request features changed, reinit the device */
>> +	if (req_features != hw->req_guest_features) {
>> +		ret = virtio_init_device(dev, req_features);
>> +		if (ret < 0)
>> +			return ret;
>> +	}
>
> Why do you have to reset virtio here? This doesn't make too much sense
> to me.
>
> IIUC, you want to make sure those TSO related features being unset at
> init time, and enable it (by doing reset) when it's asked to be enabled
> (by rte_eth_dev_configure)?
>
> Why not always setting those features? We could do the actual offloads
> when:
>
> - those features have been negoiated
>
> - they are enabled through rte_eth_dev_configure
>
> With that, I think we could avoid the reset here?

It would work for TX, since you decide to use or not the feature. But I 
think this won't work for RX: if you negociate LRO at init, the host may 
send you large packets, even if LRO is disabled in dev_configure.

Regards,
Olivier