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

[Ananyev, Konstantin]

> -----Original Message-----
> From: Yigit, Ferruh
> Sent: Wednesday, March 14, 2018 9:03 PM
> To: Ananyev, Konstantin <konstantin.ananyev at intel.com>; 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 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.

That's ok by me, but it means every PMD has to provide some preferred values?
Konstantin