Re: [dpdk-dev] [PATCH] net/virtio: remove handling of zero desc number on RxQ setup

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 9/13/21 10:25 PM, Maxime Coquelin wrote:
> 
> 
> On 8/20/21 2:47 PM, Andrew Rybchenko wrote:
>> From: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
>>
>> Rx queue setup callback allows to use the whole ring when
>> descriptor number argument equals zero. There's no point to
>> handle zero in any way since RTE Rx queue setup function
>> rte_eth_rx_queue_setup() doesn't pass zero using fallback
>> values.
>>
>> Fixes: 3be82f5cc5e3 ("ethdev: support PMD-tuned Tx/Rx parameters")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
>> Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> ---
>>  drivers/net/virtio/virtio_rxtx.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>> index 8a48fba5cc..18f03c9fc9 100644
>> --- a/drivers/net/virtio/virtio_rxtx.c
>> +++ b/drivers/net/virtio/virtio_rxtx.c
>> @@ -706,7 +706,7 @@ virtio_dev_rx_queue_setup(struct rte_eth_dev *dev,
>>  	}
>>  	vq->vq_free_thresh = rx_free_thresh;
>>  
>> -	if (nb_desc == 0 || nb_desc > vq->vq_nentries)
>> +	if (nb_desc > vq->vq_nentries)
>>  		nb_desc = vq->vq_nentries;
>>  	vq->vq_free_cnt = RTE_MIN(vq->vq_free_cnt, nb_desc);
>>  
>>
> 
> Is that really a fix?
> I see it more like an optimization in a cold path, so maybe it is not
> worth backporting?

The main idea is not an optimization, but simplification of
the code to make it easier to understand. Less special
cases is better.

I agree that it does not make sense to backport it.

> Other than that:
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Andrew.