Re: [dpdk-dev] [PATCH] ethdev: add queue state when retrieve queue information

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/22/2021 6:53 PM, Ananyev, Konstantin wrote:
> 
> 
>> -----Original Message-----
>> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> Sent: Monday, March 22, 2021 5:08 PM
>> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>; Lijun Ou <oulijun@huawei.com>;
>> thomas@monjalon.net
>> Cc: dev@dpdk.org; linuxarm@openeuler.org; Andrew Rybchenko <arybchenko@solarflare.com>; David Marchand
>> <david.marchand@redhat.com>; Ray Kinsella <mdr@ashroe.eu>; Luca Boccassi <bluca@debian.org>
>> Subject: Re: [dpdk-dev] [PATCH] ethdev: add queue state when retrieve queue information
>>
>> On 3/22/21 7:53 PM, Ananyev, Konstantin wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>>>> Sent: Monday, March 22, 2021 4:02 PM
>>>> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>; Lijun Ou <oulijun@huawei.com>;
>>>> thomas@monjalon.net
>>>> Cc: dev@dpdk.org; linuxarm@openeuler.org; Andrew Rybchenko <arybchenko@solarflare.com>; David Marchand
>>>> <david.marchand@redhat.com>; Ray Kinsella <mdr@ashroe.eu>; Luca Boccassi <bluca@debian.org>
>>>> Subject: Re: [dpdk-dev] [PATCH] ethdev: add queue state when retrieve queue information
>>>>
>>>> On 3/22/21 6:45 PM, Ananyev, Konstantin wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: dev <dev-bounces@dpdk.org> On Behalf Of Andrew Rybchenko
>>>>>> Sent: Monday, March 22, 2021 2:49 PM
>>>>>> To: Yigit, Ferruh <ferruh.yigit@intel.com>; Lijun Ou <oulijun@huawei.com>; thomas@monjalon.net
>>>>>> Cc: dev@dpdk.org; linuxarm@openeuler.org; Andrew Rybchenko <arybchenko@solarflare.com>; David Marchand
>>>>>> <david.marchand@redhat.com>; Ray Kinsella <mdr@ashroe.eu>; Luca Boccassi <bluca@debian.org>
>>>>>> Subject: Re: [dpdk-dev] [PATCH] ethdev: add queue state when retrieve queue information
>>>>>>
>>>>>> On 3/22/21 12:22 PM, Ferruh Yigit wrote:
>>>>>>> On 3/18/2021 12:25 PM, Lijun Ou wrote:
>>>>>>>> Currently, upper-layer application could get queue state only
>>>>>>>> through pointers such as dev->data->tx_queue_state[queue_id],
>>>>>>>> this is not the recommended way to access it. So this patch
>>>>>>>> add get queue state when call rte_eth_rx_queue_info_get and
>>>>>>>> rte_eth_tx_queue_info_get API.
>>>>>>>>
>>>>>>>> Note: The hairpin queue is not supported with above
>>>>>>>> rte_eth_*x_queue_info_get, so the queue state could be
>>>>>>>> RTE_ETH_QUEUE_STATE_STARTED or RTE_ETH_QUEUE_STATE_STOPPED.
>>>>>>>> Note: After add queue_state field, the 'struct rte_eth_rxq_info' size
>>>>>>>> remains 128B, and the 'struct rte_eth_txq_info' size remains 64B, so
>>>>>>>> it could be ABI compatible.
>>>>>>>>
>>>>>>>> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
>>>>>>>> Signed-off-by: Lijun Ou <oulijun@huawei.com>
>>>>>>>
>>>>>>> <...>
>>>>>>>
>>>>>>>> diff --git a/lib/librte_ethdev/rte_ethdev.h
>>>>>>>> b/lib/librte_ethdev/rte_ethdev.h
>>>>>>>> index efda313..3b83c5a 100644
>>>>>>>> --- a/lib/librte_ethdev/rte_ethdev.h
>>>>>>>> +++ b/lib/librte_ethdev/rte_ethdev.h
>>>>>>>> @@ -1591,6 +1591,8 @@ struct rte_eth_rxq_info {
>>>>>>>>        uint8_t scattered_rx;       /**< scattered packets RX supported. */
>>>>>>>>        uint16_t nb_desc;           /**< configured number of RXDs. */
>>>>>>>>        uint16_t rx_buf_size;       /**< hardware receive buffer size. */
>>>>>>>> +    /**< Queues state: STARTED(1) / STOPPED(0). */
>>>>>>>> +    uint8_t queue_state;
>>>>>>>>    } __rte_cache_min_aligned;
>>>>>>>>      /**
>>>>>>>> @@ -1600,6 +1602,8 @@ struct rte_eth_rxq_info {
>>>>>>>>    struct rte_eth_txq_info {
>>>>>>>>        struct rte_eth_txconf conf; /**< queue config parameters. */
>>>>>>>>        uint16_t nb_desc;           /**< configured number of TXDs. */
>>>>>>>> +    /**< Queues state: STARTED(1) / STOPPED(0). */
>>>>>>>> +    uint8_t queue_state;
>>>>>>>>    } __rte_cache_min_aligned;
>>>>>>>>      /* Generic Burst mode flag definition, values can be ORed. */
>>>>>>>>
>>>>>>>
>>>>>>> This is causing an ABI warning [1], but I guess it is safe since the
>>>>>>> size of the struct is not changing (cache align). Adding a few more
>>>>>>> people to comment.
>>>>>>>
>>>>>>>
>>>>>>> [1]
>>>>>>> https://travis-ci.com/github/ovsrobot/dpdk/builds/220497651
>>>>>>
>>>>>> Frankly speaking I dislike addition of queue_state as uint8_t.
>>>>>> IMHO it should be either 'bool started' or enum to support more
>>>>>> states in the future if we need.
>>>>>
>>>>> I think we already have set of defines for it:
>>>>> lib/librte_ethdev/rte_ethdev_driver.h:925:#define RTE_ETH_QUEUE_STATE_STOPPED 0
>>>>> lib/librte_ethdev/rte_ethdev_driver.h:926:#define RTE_ETH_QUEUE_STATE_STARTED 1
>>>>> lib/librte_ethdev/rte_ethdev_driver.h:927:#define RTE_ETH_QUEUE_STATE_HAIRPIN 2
>>>>>
>>>>> If we want to publish it, then might be enough just move these macros to rte_ethdev.h or so.
>>>>>
>>>>> About uint8_t vs enum - yes, in principle enum would be a bit nicer,
>>>>> but right now rte_eth_dev_data.(rx|tx)_queue_state[]  itself is an array of uint8_t.
>>>>> So probably not much point to waste extra 3B in rte_eth_(rxq|txq)_info.
>>>>> Unless in future will want to change it in struct rte_eth_dev_data too
>>>>> (or even hide it inside dev private queue data).
>>>>
>>>> I forgot about hairpin and bitmask... If so, I think it is
>>>> sufficient to fix absolutely misleading comment, say
>>>> that it is a bit mask and think about removal of
>>>> RTE_ETH_QUEUE_STATE_STOPPED (since it could be
>>>> stopped+hairpin). May be consider to use uin16_t,
>>>> since 8 bit is really small bitmask. It still fits in
>>>> available hole.
>>>
>>> Hmm, as I can read the code - hairpin queue can't be started/stopped by SW,
>>> and each of the states (stopped/started/hairpin) is mutually exclusive.
>>> Is that not what was intended when hairpin queues were introduced?
>>>
>>
>> Thanks, yes, you're right. My memory lies to me. If queue state
>> is not a bit mask, it should be an enum from API point of view.
>> Rx/Tx queue info structures are control path. I see no point to
>> save bits here. Clear API is more important on control path.
>> The only reason here to use uint8_t is to avoid ABI breakage.
>> I can't judge if it is critical to wait or not.
> 
> As alternate thought - introduce new API function,
> something like:
> int rte_eth_get_rxq_state(portid, queue_id);
> Then rte_eth_dev_is_rx_hairpin_queue() probably can be deprecated
> in favour of this new one.
> 
> 

The 'rte_eth_dev_is_rx_hairpin_queue()' is internal function, and it is not 
visible to the application, it should be OK to keep it.

But 'STATE_HAIRPIN' should be kept internal, or should be available to the 
application?

The actual need is to know the start/stop state of the queue. That is for app to 
decide if 'rte_eth_tx_done_cleanup()' can be done or not an a queue:
https://patches.dpdk.org/project/dpdk/patch/1614938252-62955-1-git-send-email-oulijun@huawei.com/

And normally I also prefer APIs with simple & clear responsibility, but this one 
seems very related to the existing '_queue_info_get()' ones, so I am fine with 
both options.