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

[Shreyansh Jain]

> -----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).

Existing example applications should be changed for this. It is tedious, but gives a true example usage.