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 1:50 PM, Ferruh Yigit wrote:
> 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.
> 

correction: it can *not* be a combination