On Wed, Feb 17, 2021 at 12:14:36PM +0000, Van Haaren, Harry wrote: > > -----Original Message----- > > From: Burakov, Anatoly <anatoly.bura...@intel.com> > > Sent: Wednesday, February 17, 2021 12:09 PM > > To: Van Haaren, Harry <harry.van.haa...@intel.com>; Richardson, Bruce > > <bruce.richard...@intel.com> > > Cc: dev@dpdk.org > > Subject: Re: [dpdk-dev] [PATCH] eal: support using 0 as coremask for no- > > affinitization > > > > On 16-Feb-21 5:44 PM, Van Haaren, Harry wrote: > > >> -----Original Message----- > > >> From: Bruce Richardson <bruce.richard...@intel.com> > > >> Sent: Tuesday, February 16, 2021 5:31 PM > > >> To: Van Haaren, Harry <harry.van.haa...@intel.com> > > >> Cc: Burakov, Anatoly <anatoly.bura...@intel.com>; dev@dpdk.org > > >> Subject: Re: [dpdk-dev] [PATCH] eal: support using 0 as coremask for no- > > >> affinitization > > >> > > >> On Tue, Feb 16, 2021 at 05:22:25PM +0000, Van Haaren, Harry wrote: > > >>>> -----Original Message----- > > >>>> From: Burakov, Anatoly <anatoly.bura...@intel.com> > > >>>> Sent: Tuesday, February 16, 2021 10:53 AM > > >>>> To: Richardson, Bruce <bruce.richard...@intel.com>; Van Haaren, Harry > > >>>> <harry.van.haa...@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. > > > > > > Ah ok, fair enough yes. > > > > > >> 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. > > > > > > Yes, correct, it would leave zero lcores for ROLE_RTE, meaning no lcores > > > for the > > application. > > > A possible solution would be to special case a zero service core mask and > > > apply > > the same > > > treatment as ROLE_RTE coremask? > > > > > > Others likely have better ideas - I don't have time to follow DPDK > > threading/pinning topic > > > closely at the moment. > > > > > > > I don't think it's a good idea to disallow service cores functionality > > in this case, but i don't have a way to solve this, other than > > implementing similar 0x0 coremask for service cores and assume it always > > means "one core affinitized to wherever the OS feels like it". After > > all, with lcore mask 0x0 we assume user wants one single core only, so > > following that, one single service core is a valid extrapolation IMO. > > OK with me - seems reasonable. > > > Perhaps specifying the number of l/s cores when using 0x0 would be > > interesting, but IMO unless there's ask for it, i'd rather not > > overcomplicate things and go with similar semantics for service cores, > > and just allow a 0x0 coremask that means only one unaffinitized service > > core will be created. > > > > Thoughts? > > Agree with keeping-it-simple if possible, and agree that unaffinitized with > a single service-core with a 0x0 mask makes sense. > > Most important to me is to maintain backward compatibility with existing > usage of -S and -s, but this shouldn't break anything? (Famous last words..) >
Not sure I entirely follow all of this. Is the suggestion just to extend -s processing to allow "0" as coremask too? That would be independent then of any core masks passed in for -c/-l options, right? As well as working well with this patch, it would also solve the issue of using single core with a coremask of e.g. 0x1 too, I think. Is my understanding correct? /Bruce
