Re: [RFC PATCH 0/7] support multi-phtread per lcore

[Bruce Richardson <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Mon, Dec 22, 2014 at 01:51:27AM +0000, Liang, Cunming wrote:
> ...
> > I'm conflicted on this one. However, I think far more applications would be
> > broken
> > to start having to use thread_id in place of an lcore_id than would be broken
> > by having the lcore_id no longer actually correspond to a core.
> > I'm actually struggling to come up with a large number of scenarios where it's
> > important to an app to determine the cpu it's running on, compared to the large
> > number of cases where you need to have a data-structure per thread. In DPDK
> > libs
> > alone, you see this assumption that lcore_id == thread_id a large number of
> > times.
> > 
> > Despite the slight logical inconsistency, I think it's better to avoid introducing
> > a thread-id and continue having lcore_id representing a unique thread.
> > 
> > /Bruce
> 
> Ok, I understand it. 
> I list the implicit meaning if using lcore_id representing the unique thread.
> 1). When lcore_id less than RTE_MAX_LCORE, it still represents the logical core id.
> 2). When lcore_id large equal than RTE_MAX_LCORE, it represents an unique id for thread.
> 3). Most of APIs(except rte_lcore_id()) in rte_lcore.h suggest to be used only in CASE 1)
> 4). rte_lcore_id() can be used in CASE 2), but the return value no matter represent a logical core id.
> 
> If most of us feel it's acceptable, I'll prepare for the RFC v2 base on this conclusion.
> 
> /Cunming

Sorry, I don't like that suggestion either, as having lcore_id values greater
than RTE_MAX_LCORE is terrible, as how will people know how to dimension arrays
to be indexes by lcore id? Given the choice, if we are not going to just use
lcore_id as a generic thread id, which is always between 0 and RTE_MAX_LCORE
we can look to define a new thread_id variable to hold that. However, it should
have a bounded range.
>From an ease-of-porting perspective, I still think that the simplest option is to
use the existing lcore_id and accept the fact that it's now a thread id rather
than an actual physical lcore. Question is, is would that cause us lots of issues
in the future?

/Bruce