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

[Stephen Hemminger <stephen@networkplumber.org>]

On Mon, 22 Dec 2014 09:46:03 +0000
Bruce Richardson <bruce.richardson@intel.com> wrote:

> 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

The current rte_lcore_id() has different meaning the thread. Your proposal will
break code that uses lcore_id to do per-cpu statistics and the lcore_config
code in the samples.
q