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

[Juraj Linkeš]

> -----Original Message-----
> From: Thomas Monjalon <thomas at monjalon.net>
> Sent: Monday, November 16, 2020 10:24 AM
> To: Bruce Richardson <bruce.richardson at intel.com>
> Cc: Juraj Linkeš <juraj.linkes at pantheon.tech>; Ruifeng.Wang at arm.com;
> Honnappa.Nagarahalli at arm.com; Phil.Yang at arm.com;
> vcchunga at amazon.com; Dharmik.Thakkar at arm.com; jerinjacobk at gmail.com;
> hemant.agrawal at nxp.com; ajit.khaparde at broadcom.com;
> ferruh.yigit at intel.com; dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v12 09/14] build: optional NUMA and cpu counts
> detection
> 
> 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.
3. Detected values will be used for native build when the value is -1.

The description is a bit longer because of this and I've already tried to shorten it by combining 1 and 2 into one sentence. But maybe we can shorten it while making it a bit clearer. I'll think about it.

> > As I flagged in a previous mail thread, the whole config of DPDK
> > builds is something we need to take a bigger look at in 21.02 and beyond.
> 
> Yes definitely.
> 
>