Re: [dpdk-dev] [PATCH 3/3] net/virtio: reject unsupported Rx multi queue modes

[Andrew Rybchenko <arybchenko@solarflare.com>]

@Thomas, @Ferruh, please see small question below.

On 10/9/19 1:41 PM, Tiwei Bie wrote:
> On Wed, Oct 09, 2019 at 12:00:28PM +0300, Andrew Rybchenko wrote:
>> On 10/9/19 11:43 AM, Tiwei Bie wrote:
>>> On Wed, Oct 09, 2019 at 11:04:38AM +0300, Andrew Rybchenko wrote:
>>>> On 10/8/19 8:46 AM, Tiwei Bie wrote:
>>>>> On Tue, Oct 01, 2019 at 04:44:31PM +0100, Andrew Rybchenko wrote:
>>>>>> From: Dilshod Urazov <Dilshod.Urazov@oktetlabs.ru>
>>>>>>
>>>>>> This driver supports none of DCB, RSS or VMDQ modes,
>>>>>> therefore must check and return error if configured incorrectly.
>>>>>>
>>>>>> Fixes: c1f86306a026 ("virtio: add new driver")
>>>>>> Cc: stable@dpdk.org
>>>>>>
>>>>>> Signed-off-by: Dilshod Urazov <Dilshod.Urazov@oktetlabs.ru>
>>>>>> Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
>>>>>> ---
>>>>>>     drivers/net/virtio/virtio_ethdev.c | 7 +++++++
>>>>>>     1 file changed, 7 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
>>>>>> index 7261109dd..0af4fc392 100644
>>>>>> --- a/drivers/net/virtio/virtio_ethdev.c
>>>>>> +++ b/drivers/net/virtio/virtio_ethdev.c
>>>>>> @@ -2071,6 +2071,13 @@ virtio_dev_configure(struct rte_eth_dev *dev)
>>>>>>     	PMD_INIT_LOG(DEBUG, "configure");
>>>>>>     	req_features = VIRTIO_PMD_DEFAULT_GUEST_FEATURES;
>>>>>> +	if (rxmode->mq_mode != ETH_MQ_RX_NONE) {
>>>>>> +		PMD_DRV_LOG(ERR,
>>>>>> +			"Unsupported Rx multi queue mode %d",
>>>>>> +			rxmode->mq_mode);
>>>>>> +		return -EINVAL;
>>>>>> +	}
>>>>> We need similar checks for Tx as well.
>>>> OK, I'll add.
>>>>
>>>> However, I'm not 100% sure about RSS. Yes, I know that virtio has
>>>> no RSS configuration support, but it looks possible to have multi queue
>>>> in vhost-net case.
>>> Yeah, it's possible to have MQ in virtio.
>>> The RSS support in virtio is still WIP.
>>> https://github.com/oasis-tcs/virtio-spec/issues/48
>> Thanks for the link. So, may be ETH_MQ_RX_RSS should be accepted
>> as well, but attempts to configure RSS rejected?
>> Yes, it is a bit strange to accept RSS with empty rss_hf etc, but
>> at least it is exactly what net/virtio can do.
>>
>> And one more thought...
>> It looks like if more than one Rx queue is configured, mq_mode must
>> be ETH_MQ_RX_RSS and must not be ETH_MQ_RX_NONE.
> Some apps in DPDK will set mq_mode to ETH_MQ_RX_NONE while
> enabling multiple queue pairs, e.g.:
>
> https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L137
> https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L181-L182
> https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L3938-L3948
>
> Testpmd will also set mq_mode to ETH_MQ_RX_NONE when multiple
> Rx queues are enabled but rss_hf is empty:
>
> https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test-pmd/testpmd.c#L2935-L2938
> https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test-pmd/testpmd.c#L2945-L2948
> (the flow_type_rss_offloads reported by virtio-PMD is zero)
>
> My understanding is that, setting mq_mode to ETH_MQ_RX_NONE means
> no method is enforced on how to route packets to MQs.

I'm not sure. It is definitely a place to be improved in
ethdev documentation. Thomas, Ferruh, what do you think?
Is it really a definition of ETH_MQ_RX_NONE?

> It looks that ETH_MQ_RX_NONE is the best fit for virtio currently.

Anyway I agree and I think it is better to go this way in the patch.

Thanks,
Andrew.