Re: [dpdk-dev] [PATCH] eal: support using 0 as coremask for no-affinitization

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Feb 16, 2021 at 05:22:25PM +0000, Van Haaren, Harry wrote:
> > -----Original Message-----
> > From: Burakov, Anatoly <anatoly.burakov@intel.com>
> > Sent: Tuesday, February 16, 2021 10:53 AM
> > To: Richardson, Bruce <bruce.richardson@intel.com>; Van Haaren, Harry
> > <harry.van.haaren@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH] eal: support using 0 as coremask for no-
> > affinitization
> >
> > On 16-Feb-21 10:46 AM, Bruce Richardson wrote:
> > > On Tue, Feb 16, 2021 at 10:36:13AM +0000, Burakov, Anatoly wrote:
> > >> On 16-Feb-21 9:43 AM, Bruce Richardson wrote:
> > >>> Allow the user to specify that they don't want any core pinning from DPDK
> > >>> by passing in the coremask of 0.
> > >>> ---
> > >>
> > >> I haven't checked what happens yet, but down the line we also set affinity
> > >> for service cores as well as interrupt thread. what would be the semantics
> > >> of those in this particular case? do we want the same ability for service
> > >> cores (i.e. pick a non-affinitized core)? And where does interrupt thread
> > >> affinitize in this case (presumably, nowhere too)?
> > >>
> > > I have not checked the service core setup, because a) I forgot about them
> > > and b) I'm not sure how their affinity rules work with respect to the main
> > > lcore mask. On the other hand I did check out that the lcore mask for all
> > > non-pinned threads, or control threads, is the full set of bits as
> > > expected.
> > >
> > > /Bruce
> > >
> >
> > +Harry,
> >
> > I believe service core mask must not overlap with lcore masks, so
> > presumably using 0 as lcore mask would make it so that any service core
> > mask will be valid (which is presumably what we want?).
> 
> Services cores -S list or -s <mask> *must* overlap with the RTE lcores, EAL
> then"steals" the service cores from the application lcores, code that implements here:
> http://git.dpdk.org/dpdk-stable/tree/lib/librte_eal/common/eal_common_options.c?h=20.11#n657
> 
> > Should service cores also have a "just pick a core" parameter?
> 
> I'm not sure, depends on what the bigger goal is here.
> Assuming we're enabling this for ROLE_RTE threads, then
> it would seem to me that ROLE_SERVICE and control threads
> would require similar treatment?
> 
Control threads are affinitised to all cores not in the coremask, which
means in this case that they can run anywhere on the system the OS chooses.
In case of service cores, it would seem that using service cores with an
empty coremask is just not compatible. I would assume that this
incompatibility already exists when one has a coremask with only one core
already in it.

/Bruce