[dpdk-dev] [PATCH v3 1/4] ethdev: add a field for rxq info structure

[Chengchang Tang]

Hi, Matan

On 2020/9/1 23:33, Matan Azrad wrote:
> 
> Hi Chengchang
> 
> Please see some question below.
> 
> From: Chengchang Tang
>> Add a field named rx_buf_size in rte_eth_rxq_info to indicate the buffer size
>> used in receiving packets for HW.
>>
>> In this way, upper-layer users can get this information by calling
>> rte_eth_rx_queue_info_get.
>>
>> Signed-off-by: Chengchang Tang <tangchengchang at huawei.com>
>> Reviewed-by: Wei Hu (Xavier) <xavier.huwei at huawei.com>
>> Acked-by: Andrew Rybchenko <arybchenko at solarflare.com>
>> ---
>>  lib/librte_ethdev/rte_ethdev.h | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
>> index 70295d7..9fed5cb 100644
>> --- a/lib/librte_ethdev/rte_ethdev.h
>> +++ b/lib/librte_ethdev/rte_ethdev.h
>> @@ -1420,6 +1420,8 @@ struct rte_eth_rxq_info {
>>         struct rte_eth_rxconf conf; /**< queue config parameters. */
>>         uint8_t scattered_rx;       /**< scattered packets RX supported. */
>>         uint16_t nb_desc;           /**< configured number of RXDs. */
>> +       /**< buffer size used for hardware when receive packets. */
>> +       uint16_t rx_buf_size;
> 
> Is it the maximum supported Rx buffer by the HW?
> If yes, maybe max_rx_buf_size is better name?

No, it is the Rx buffer size currently used by HW.

IMHO, the structure rte_eth_rxq_info and associated query API are mainly used to query HW configurations
at runtime or after queue is configured/setup. Therefore, the content of this structure should be the
current HW configuration.

> Maybe document that 0 means - no limitation by HW?

Yes, there is no need to fill this filed for HW that has no restrictions on it.
I'll add it in v4.

> Must application read it in order to know if its datapath should handle multi-segment buffers?

I think it's more appropriate to use scattered_rx to determine if multi-segment buffers should be handled.

> 
> Maybe it will be good to force application to configure scatter when this field is valid and smaller than max_rx_pkt_len\max_lro.. (<= room size)...
> 
> 
>>  } __rte_cache_min_aligned;
>>
>>  /**