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

Walukiewicz, Miroslaw Miroslaw.Walukiewicz at intel.com
Mon Dec 22 11:01:38 CET 2014


> -----Original Message-----
> From: Richardson, Bruce
> Sent: Monday, December 22, 2014 10:46 AM
> To: Liang, Cunming
> Cc: Walukiewicz, Miroslaw; dev at dpdk.org
> Subject: Re: [dpdk-dev] [RFC PATCH 0/7] support multi-phtread per lcore
> 
> 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?
> 
I would prefer keeping the RTE_MAX_LCORES as Bruce suggests and 
determine the HW core on base of following condition if we really have to know this.

int num_cores_online = count of cores encountered in the core mask provided by cmdline parameter

Rte_lcore_id() < num_cores_online -> physical core (pthread first started on the core)

Rte_lcore_id() >= num_cores_online -> pthread created by rte_pthread_create

Mirek

> /Bruce


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