Re: [dpdk-dev] [PATCH v12 09/14] build: optional NUMA and cpu counts detection

[Juraj Linkeš <juraj.linkes@pantheon.tech>]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Wednesday, November 18, 2020 3:43 PM
> To: Bruce Richardson <bruce.richardson@intel.com>; Juraj Linkeš
> <juraj.linkes@pantheon.tech>
> Cc: Ruifeng.Wang@arm.com; Honnappa.Nagarahalli@arm.com;
> Phil.Yang@arm.com; vcchunga@amazon.com; Dharmik.Thakkar@arm.com;
> jerinjacobk@gmail.com; hemant.agrawal@nxp.com;
> ajit.khaparde@broadcom.com; ferruh.yigit@intel.com; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v12 09/14] build: optional NUMA and cpu counts
> detection
> 
> 18/11/2020 15:19, Juraj Linkeš:
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 16/11/2020 10:13, Bruce Richardson:
> > > > On Mon, Nov 16, 2020 at 08:24:48AM +0100, Thomas Monjalon wrote:
> > > > > 13/11/2020 15:31, Juraj Linkeš:
> > > > > > +option('max_lcores', type: 'integer', value: 0,
> > > > > > +	description: 'maximum number of cores/threads supported by
> EAL.
> > > > > > +Set to positive integer to overwrite per-arch or
> > > > > > +cross-compilation
> > > defaults. Set to -1 to detect the number of cores on the build
> > > machine.') option('max_numa_nodes', type: 'integer', value: 0,
> > > > > > +	description: 'maximum number of NUMA nodes supported by
> EAL.
> > > > > > +Set to positive integer to overwrite per-arch or
> > > > > > +cross-compilation defaults. Set to -1 to detect the number of
> > > > > > +numa nodes on the build machine.')
> > > > >
> > > > > First comment: I don't like having so long description.
> > > > > Second: I don't understand.
> > > > >
> > > > > It is said the default value is 0 so I expect it means automatic detection.
> > > > > But later it is said -1 is for detection. So ?
> > > > >
> > > > Zero is for the "per-arch or cross-compilation default". This was
> > > > discussed quite a bit in previous versions and this was te best
> > > > compromise we could come up with. Having a default of auto-detect
> > > > is definitely not something I think we should go with - just
> > > > thinking of all the build CI jobs running on
> > > > 2 or 4 core VMs! However, Juraj really felt there was value in
> > > > having auto-detection, so it's set as a -1 value, which I'm ok with.
> > >
> > > The problem is that I don't understand what 0 means.
> > >
> >
> > There are three pieces of information which we need to convey:
> > 1. The default value (0) indicates that per-arch or cross-compilation defaults
> will be used.
> > 2. Positive integer values will be used instead of these defaults.
> 
> Where these positive values come from?
> 

From the user - they will have the option to set it to whatever the like if they don't want to use defaults.

> > 3. Detected values will be used for native build when the value is -1.
> 
> Why not detect for any native build set up with 0 (default)?
> 

I'll let Bruce explain this, but I'll just say that we wanted to make the detection the default for native builds, so we're in agreement.