Re: [dpdk-dev] [RFC v2 1/3] ethdev: add the API for getting trace information

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

On 9/9/2019 1:40 PM, Bruce Richardson wrote:
> On Mon, Sep 09, 2019 at 12:23:36PM +0100, Ferruh Yigit wrote:
>> On 9/7/2019 3:42 AM, Wang, Haiyue wrote:
>>>> -----Original Message-----
>>>> From: Yigit, Ferruh
>>>> Sent: Friday, September 6, 2019 22:22
>>>> To: Ray Kinsella <mdr@ashroe.eu>; Wang, Haiyue <haiyue.wang@intel.com>
>>>> Cc: dev@dpdk.org
>>>> Subject: Re: [dpdk-dev] [RFC v2 1/3] ethdev: add the API for getting trace information
>>>>
>>>> On 8/13/2019 1:51 PM, Ray Kinsella wrote:
>>>>>
>>>>>
>>>>> On 13/08/2019 04:24, Stephen Hemminger wrote:
>>>>>> On Tue, 13 Aug 2019 11:06:10 +0800
>>>>>> Haiyue Wang <haiyue.wang@intel.com> wrote:
>>>>>>
>>>>>>> Enhance the PMD to support retrieving trace information like
>>>>>>> Rx/Tx burst selection etc.
>>>>>>>
>>>>>>> Signed-off-by: Haiyue Wang <haiyue.wang@intel.com>
>>>>>>> ---
>>>>>>>  lib/librte_ethdev/rte_ethdev.c      | 18 ++++++++++++++++++
>>>>>>>  lib/librte_ethdev/rte_ethdev.h      |  9 +++++++++
>>>>>>>  lib/librte_ethdev/rte_ethdev_core.h |  4 ++++
>>>>>>>  3 files changed, 31 insertions(+)
>>>>>>>
>>>>>>> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
>>>>>>> index 17d183e..6098fad 100644
>>>>>>> --- a/lib/librte_ethdev/rte_ethdev.c
>>>>>>> +++ b/lib/librte_ethdev/rte_ethdev.c
>>>>>>> @@ -4083,6 +4083,24 @@ rte_eth_tx_queue_info_get(uint16_t port_id, uint16_t queue_id,
>>>>>>>  }
>>>>>>>
>>>>>>>  int
>>>>>>> +rte_eth_trace_info_get(uint16_t port_id, uint16_t queue_id,
>>>>>>> +		       enum rte_eth_trace type, char *buf, int sz)
>>>>
>>>> Better to use struct as argument instead of individual variables because it is
>>>> easier to extend the struct later if needed.
>>>>
>>>>>>> +{
>>>>>>> +	struct rte_eth_dev *dev;
>>>>>>> +
>>>>>>> +	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
>>>>>>> +
>>>>>>> +	if (buf == NULL)
>>>>>>> +		return -EINVAL;
>>>>>>> +
>>>>>>> +	dev = &rte_eth_devices[port_id];
>>>>>>> +
>>>>>>> +	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->trace_info_get, -ENOTSUP);
>>>>>>> +
>>>>>>> +	return dev->dev_ops->trace_info_get(dev, queue_id, type, buf, sz);
>>>>>>
>>>>>> What if queueid is out of bounds?
>>>>>>
>>>>>> The bigger problem is that this information is like a log message
>>>>>> and unstructured, which makes it device specific and useless for automation.
>>>>>
>>>>> IMHO - this is much better implemented as a capability bitfield, that
>>>>> can be queried.
>>>>
>>>> +1 to return the datapath capability as bitfield.
>>>>
>>>> Also +1 to have a new API,
>>>> - I am not sure about the API name, 'rte_eth_trace_info_get()', can we find
>>>> something better instead of 'trace' there.
>>>> - I think we should limit this API only to get current datapath configuration,
>>>> for clarity of the API don't return capability or not datapath related config.
>>>>
>>>> Also this information not always supported in queue level, what do you think
>>>> having ability to get this information in port level,
>>>> like this API can return a struct, which may have a field that says if the
>>>> output is for queue or port, or this can be another bitfield, what do you think?
>>>>
>>>
>>> #define RX_SCALAR	(1ULL < 0)
>>> #define RX_VECTOR_AVX2  ...
>>
>> What about having RX_VECTOR value, later another bit group for the details of
>> the vectorization:
>> SSE
>> AVX2
>> AVX512
>> NEON
>> ALTIVEC
>>
>> Since above options can exist together, what about using values for them instead
>> of bitfields? Reserving 4 bits, 2^4 = 16, can be enough I think for long term.
>>
> Rather than having named vector types, we just need to worry about the ones
> for the current architecture. Therefore I'd suggest just using vector
> widths, one bit each for 16B, 32B and 64B vector support. For supporting
> multiple values, 16 combinations is not enough for all the possibilities.
> 

vector width can be an option too, no objection there. But this is only for
current configuration, so it can be a combination, we have now 5 types and
allocating space for 16.