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

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

On 9/10/2019 3:19 PM, Wang, Haiyue wrote:
>> -----Original Message-----
>> From: Yigit, Ferruh
>> Sent: Tuesday, September 10, 2019 17:15
>> To: Wang, Haiyue <haiyue.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
>> Cc: Ray Kinsella <mdr@ashroe.eu>; dev@dpdk.org; Sun, Chenmin <chenmin.sun@intel.com>
>> Subject: Re: [dpdk-dev] [RFC v2 1/3] ethdev: add the API for getting trace information
>>
>> On 9/10/2019 9:37 AM, Wang, Haiyue wrote:
>>>> -----Original Message-----
>>>> From: Yigit, Ferruh
>>>> Sent: Tuesday, September 10, 2019 16:07
>>>> To: Wang, Haiyue <haiyue.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>
>>>> Cc: Ray Kinsella <mdr@ashroe.eu>; dev@dpdk.org; Sun, Chenmin <chenmin.sun@intel.com>
>>>> Subject: Re: [dpdk-dev] [RFC v2 1/3] ethdev: add the API for getting trace information
>>>>
>>>> On 9/10/2019 5:36 AM, Wang, Haiyue wrote:
>>>>> Thanks Ferruh, Bruce.
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Yigit, Ferruh
>>>>>> Sent: Monday, September 9, 2019 21:18
>>>>>> To: Richardson, Bruce <bruce.richardson@intel.com>
>>>>>> Cc: Wang, Haiyue <haiyue.wang@intel.com>; Ray Kinsella <mdr@ashroe.eu>; dev@dpdk.org; Sun,
>> Chenmin
>>>>>> <chenmin.sun@intel.com>
>>>>>> Subject: Re: [dpdk-dev] [RFC v2 1/3] ethdev: add the API for getting trace information
>>>>>>
>>>>>> 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.
>>>>>>>>
>>>>>>>
>>>>>
>>>>> enum rte_eth_burst_mode_option {
>>>>> 	BURST_SCALAR = (1 << 0),
>>>>> 	BURST_VECTOR = (1 << 1),
>>>>>
>>>>> 	BURST_VECTOR_MODE_MASK = (0x3F << 2),
>>>>> 	BURST_ALTIVEC          = (1 << 2),
>>>>> 	BURST_NEON             = (2 << 2),
>>>>> 	BURST_SSE              = (3 << 2),
>>>>> 	BURST_AVX2             = (4 << 2),
>>>>> 	BURST_AVX512           = (5 << 2),
>>>>
>>>> Do we need to have bitfields for this, I was suggesting reserve 4 bits, bit 2-5
>>>> (inclusive) and use their value:
>>>>
>>>> BURST_VECTOR_MODE_IDX  = 2
>>>> BURST_VECTOR_MODE_SIZE = 4
>>>> BURST_VECTOR_MODE_MASK =
>>>> 	((1 << BURST_VECTOR_MODE_SIZE) - 1) << BURST_VECTOR_MODE_IDX
>>>>
>>>> vector_mode = (options & BURST_VECTOR_MODE_MASK) >> BURST_VECTOR_MODE_IDX
>>>>
>>>> if (vector_mode == 0) // BURST_SSE
>>>> if (vector_mode == 1) // BURST_AVX2
>>>> if (vector_mode == 2) // BURST_AVX512
>>>> if (vector_mode == 3) // BURST_NEON
>>> }
>>>
>>
>> I can see how you intended use it, only they don't need to be bitfield and using
>> with value saves bits.
>> Also I think good to reserve some bits for future modes.
>>
> 
> I think I understand your 'value saves bits' concern now:
> 
> What you mentioned value such as 1, 2, 3 has been *shifted* as new options: (1 << 2),
> (2 << 2), (3 << 2). The *shifted* value seems be easily for using, like, you don't
> need to re-define another enum like enum ...vector_mode { SSE, AVX2 } for accessing.
> And we can extract the vector mode easy: options & BURST_VECTOR_MODE_MASK, no need to
> shift right again for getting the pure number. And for displaying name, it also should
> be consistent:
> 	...
> 	case RTE_ETH_BURST_VECTOR: return "Vector";
> 	case RTE_ETH_BURST_ALTIVEC: return "AltiVec";
> 	case RTE_ETH_BURST_NEON: return "Neon";
> 

Yep, this is what I was suggesting, agree that bitwise is a little easier, and
specially after having separate Rx/Tx APIs there are enough room in the
variable, so ok with your suggestion.
But please reserve some additional room future vectorisation modes, I would say
overall 14 would be good, so first word can be for modes.