[dpdk-dev] [RFC PATCH v1 1/4] ethdev: add support for PMD-tuned Tx/Rx parameters

[Ferruh Yigit]

On 3/15/2018 2:39 PM, Bruce Richardson wrote:
> On Thu, Mar 15, 2018 at 01:57:13PM +0000, Ferruh Yigit wrote:
>> On 3/14/2018 9:36 PM, Bruce Richardson wrote:
>>> On Wed, Mar 14, 2018 at 09:02:47PM +0000, Ferruh Yigit wrote:
>>>> On 3/14/2018 6:53 PM, Ananyev, Konstantin wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ferruh Yigit
>>>>>> Sent: Wednesday, March 14, 2018 5:52 PM
>>>>>> To: Shreyansh Jain <shreyansh.jain at nxp.com>; Horton, Remy <remy.horton at intel.com>; dev at dpdk.org
>>>>>> Cc: Lu, Wenzhuo <wenzhuo.lu at intel.com>; Wu, Jingjing <jingjing.wu at intel.com>; Zhang, Qi Z <qi.z.zhang at intel.com>; Xing, Beilei
>>>>>> <beilei.xing at intel.com>; Thomas Monjalon <thomas at monjalon.net>
>>>>>> Subject: Re: [dpdk-dev] [RFC PATCH v1 1/4] ethdev: add support for PMD-tuned Tx/Rx parameters
>>>>>>
>>>>>> On 3/14/2018 5:23 PM, Shreyansh Jain wrote:
>>>>>>>> -----Original Message-----
>>>>>>>> From: Ferruh Yigit [mailto:ferruh.yigit at intel.com]
>>>>>>>> Sent: Wednesday, March 14, 2018 10:13 PM
>>>>>>>> To: Remy Horton <remy.horton at intel.com>; dev at dpdk.org
>>>>>>>> Cc: Wenzhuo Lu <wenzhuo.lu at intel.com>; Jingjing Wu
>>>>>>>> <jingjing.wu at intel.com>; Qi Zhang <qi.z.zhang at intel.com>; Beilei Xing
>>>>>>>> <beilei.xing at intel.com>; Shreyansh Jain <shreyansh.jain at nxp.com>;
>>>>>>>> Thomas Monjalon <thomas at monjalon.net>
>>>>>>>> Subject: Re: [dpdk-dev] [RFC PATCH v1 1/4] ethdev: add support for PMD-
>>>>>>>> tuned Tx/Rx parameters
>>>>>>>>
>>>>>>>> On 3/14/2018 3:48 PM, Remy Horton wrote:
>>>>>>>>>
>>>>>>>>> On 14/03/2018 14:43, Ferruh Yigit wrote:
>>>>>>>>> [..]
>>>>>>>>>>>  lib/librte_ether/rte_ethdev.c | 18 ++++++++++++++++++
>>>>>>>>>>>  lib/librte_ether/rte_ethdev.h | 15 +++++++++++++++
>>>>>>>>>>
>>>>>>>>>> Can you please remove deprecation notice in this patch.
>>>>>>>>>
>>>>>>>>> Done.
>>>>>>>>>
>>>>>>>>>>> +	/* Defaults for drivers that don't implement preferred
>>>>>>>>>>> +	 * queue parameters.
>>>>>>>>> [..]
>>>>>>>>>> Not sure about having these defaults here. It is OK to have defaults
>>>>>>>> in driver,
>>>>>>>>>> in application or in config file, but I am not sure if putting them
>>>>>>>> into device
>>>>>>>>>> abstraction layer hides them.
>>>>>>>>>>
>>>>>>>>>> What about not providing any default in ethdev layer, and get zero
>>>>>>>> as invalid
>>>>>>>>>> when using them?
>>>>>>>>>
>>>>>>>>> This is something I have been thinking about, and I am going to
>>>>>>>> remove
>>>>>>>>> them for the V2. Original motive was to avoid breaking testpmd for
>>>>>>>> PMDs
>>>>>>>>> that don't give defaults (i.e. almost all of them). The alternative
>>>>>>>> is
>>>>>>>>> to put place-holders into all the PMDs themselves, but I am not sure
>>>>>>>> if
>>>>>>>>> this is appropriate.
>>>>>>>>
>>>>>>>> I think preferred values should be optional, PMD should have right to
>>>>>>>> not
>>>>>>>> provide any. Implementation in 4/4 forces preferred values, either in
>>>>>>>> all PMDs
>>>>>>>> or in ethdev layer.
>>>>>>>>
>>>>>>>> What about changing approach in application:
>>>>>>>>  is preferred value provided [1] ?
>>>>>>>>   yes => use it by sending value 0
>>>>>>>>   no => use application provided value, same as now, so control should
>>>>>>>> be in
>>>>>>>> application.
>>>>>>>>
>>>>>>>> I am aware this breaks the comfort of just providing 0 and PMD values
>>>>>>>> will be
>>>>>>>> used but covers the case there is no PMD values.
>>>>>>>>
>>>>>>>> [1]
>>>>>>>> it can be possible to check if preferred value provided by comparing 0,
>>>>>>>> but if 0
>>>>>>>> is a valid value that can be problem. It may not be problem with
>>>>>>>> current
>>>>>>>> variables but it may be when this struct extended, it may be good to
>>>>>>>> think about
>>>>>>>> alternative here.
>>>>>>>
>>>>>>> I don't think we should use the condition of "yes => use it by sending value 0". That is non-intuitive. Ideally, the application should query
>>>>>> and then if query responds with value as '0' (which can be valid for some variables in future), it sends its own value to setup functions
>>>>>> (whether '0' or something else, in case of 0 response, would depend on the knob).
>>>>>>
>>>>>> Right, at that stage application already knows what is the preferred value and
>>>>>> can directly use it.
>>>>>>
>>>>>>
>>>>>> Will it be too much to:
>>>>>>
>>>>>> 1) Adding a new field into "rte_eth_[rt]xconf" to say if exists prefer PMD
>>>>>> values. "prefer_device_values" ?
>>>>>> Application can provide values as usual, but if that field is set, abstraction
>>>>>> layer overwrites the application values with PMD preferred ones. If there is no
>>>>>> PMD preferred values continue using application ones.
>>>>>>
>>>>>>
>>>>>> 2) Add a bitwise "is_set" field to new "preferred_size" struct, which may show
>>>>>> status of other fields in the struct, if PMD set a valid value for them or not,
>>>>>> so won't have to rely on the 0 check.
>>>>>
>>>>> That all seems like too much hassle for such small thing.
>>>>
>>>> Fair enough.
>>>>
>>>>> If we really want to allow PMD not to provide preferred values -
>>>>> then instead of adding rte_eth_dev_pref_info into dev_info we can simply
>>>>> introduce a new optional ethdev API call:
>>>>> rte_eth_get_pref_params() or so.
>>>>> If the PMD doesn’t want to provide preferred params to the user it simply
>>>>> wouldn't implement that function. 
>>>>
>>>> Same can be done with updated rte_eth_dev_info.
>>>> Only application needs to check and use PMD preferred values, so this will mean
>>>> dropping "pass 0 to get preferred values" feature in initial set.
>>>>
>>>>>
>>> I actually don't see the issue with having ethdev provide reasonable
>>> default values. If those don't work for a driver, then let the driver
>>> provide it's own values. If the defaults don't work for an app, then let
>>> the app override the provided values.
>>>
>>> It really is going to make the app writers job easier if we do things this
>>> way. The only thing you are missing is the info as to whether it's ethdev
>>> or the driver that's providing the values, but in the case that it's
>>> ethdev, then the driver by definition "doesn't care", so we can treat them
>>> as driver provided values. What's the downside?
>> Abstraction layer having hardcoded config options doesn't look right to me. In
>> long term who will ensure to make those values relevant?
>>
> 
> Let me turn that question around - in the long-term how likely are the
> values to change significantly? Also, long-term all PMDs should provide
> their own default values and then we can remove the values in the ethdev
> layer.
> 
>> When application provides a value of 0, it won't know if it is using PMD
>> preferred values or some other defaults, what if application explicitly wants
>> use PMD preferred values?
> 
> If the PMD has preferred values, they will be automatically used. Is there
> are case where the app would actually care about it? If the driver doesn't
> provide default values, how is the app supposed to know what the correct
> value for that driver is? And if the app *does* know what the best value
> for a driver is - even if the driver itself doesn't, it can easily detect
> when a port is using the driver and provide it's own ring setup defaults.
> If you want, we can provide a flag field to indicate that fields are ethdev
> defaults not driver defaults or something, but I'm struggling to come up
> with a scenario where it would make a practical difference to an app.
> 
>>
>> The new fields are very similar to "default_[rt]xconf" in dev_info. Indeed
>> perhaps we should use same naming convention because intention seems same.
>> And we can continue to use new fields same as how "default_[rt]xconf" used.
>>
>> What about having something like rte_eth_tx_queue_setup_relaxed() where
>> application really don't care about values, not sure why, which can get config
>> values as much as from PMDs and fill the missing ones with the values defined in
>> function?
>>
> 
> Or how about having the ethdev defaults in the rx/tx setup function instead
> of in the dev_info one? If user specifies a zero size, we use the dev_info
> value if provided by driver, otherwise ethdev default. That allows the
> majority of apps to never worry about ring sizes, but for those that do,
> they can query the driver defaults directly, or if not present set their
> own.

OK this at least gives a way to application to know where defaults are coming from.


Hi Remy, Shreyansh,

What do you think about using a variable name consistent with existing
"default_[rt]xconf" in dev_info?

> 
> /Bruce
>