Re: [dpdk-dev] [PATCH v5] sched: make RED scaling configurable

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Dumitrescu,
> Cristian
> Sent: Friday, January 12, 2018 11:09 AM
> To: Dewar, Alan <ad759e@intl.att.com>; 'alangordondewar@gmail.com'
> <alangordondewar@gmail.com>
> Cc: 'dev@dpdk.org' <dev@dpdk.org>; 'Alan Dewar' <alan.dewar@att.com>;
> Kantecki, Tomasz <tomasz.kantecki@intel.com>; Singh, Jasvinder
> <jasvinder.singh@intel.com>
> Subject: Re: [dpdk-dev] [PATCH v5] sched: make RED scaling configurable
> 
> ...<snip>
> 
> > > > diff --git a/lib/librte_sched/rte_red.c b/lib/librte_sched/rte_red.c
> > > > +int
> > > > +rte_red_set_scaling(uint16_t max_red_queue_length) {
> > > > +	int8_t count;
> > > > +
> > > > +	if (rte_red_init_done)
> > > > +		/**
> > > > +		 * Can't change the scaling once the red table has been
> > > > +		 * computed.
> > > > +		 */
> > > > +		return -1;
> > >
> > > Is there a reason why we cannot simply reset the scaling here?
> >
> > Actually we could, but I was originally thinking that you might be happier
> > keeping with a one-time RED initialization function, but then had to
> > introduce the rte_reset_red_scaling function for the unit-tests. I'm happy
> to
> > do RED reinitialization here, if you are.
> >
> 
> Hi Alan,
> 
> What is the intention of the new rte_red_set_scaling() function?
> 	1. Is it to be called only once, before any RED object gets created?
> 	2. Is it possible to call it post-init, but in this case any RED object
> already created are not impacted (they continue to work)?
> 
> If the answer is 2, then yes, we could simply drop the __rte_red_reset() and
> do the RED globals reset as part of the rte_red_set_scaling() function
> transparently.
> 
> If the answer is 1, then we probably need to keep your approach: we need a
> global rte_red_init_done flag, and rte_red_set_scaling() could only be called
> at init time before any red objects are created.
> 
> I probably need to spend more time assessing all the code implications.
> 
> Regards,
> Cristian

Hi Alan,

After talking to Tomasz, we agreed that 2. Is not an option, as any previously created red object will be broken.

So 1. Is the right answer, therefore this function can be called only once and only before any red objects are created. So, IMO we should do this:
-when rte_red_init_done is true, we need to return error
-when rte_red_init_done is false, we need to perform red initialization and set this flag

Agree?

Please also add a comment in the Doxygen description of rte_red_set_caling() in the rte_red.h file, stating that this function can be called only once and only before any red objects are created.

Regards,
Cristian