Re: [dpdk-dev] [PATCH] vdpa/mlx5: use master core Id for vhost thread

[David Marchand <david.marchand@redhat.com>]

On Tue, Jul 28, 2020 at 9:30 AM Matan Azrad <matan@mellanox.com> wrote:
> > > > rte_lcore_to_cpu_id(-1) is supposed to return the current lcore id.
> > > > As explained in the commitlog of 67ae5936c4fc36, for a non-EAL
> > > > thread (which has no associated lcore by default) calling this
> > > > function means lcore_config[-1].core_id.
> > >
> > > Deosn't lcore mean core?
> >
> > No.
>
> So, it may be that we have more than one lcore working on a specific cpu_id?
> Can you extend here?

A control thread is a non-EAL thread.
A non-EAL thread has no lcore associated (unless you call the newly
added rte_thread_register API).

Not sure why you need the physical core identifier in the driver.

It is possible that non-EAL threads run on one physical core if you
start your application with the right cpuset.
But without checking, you can't make such an assumption.


>
> >
> > > So, if the private thread run on a core that opened by EAL, Shouldn't
> > > the API return the lcore of the private thread core?
> >
> > vhost-events is a control thread.
> > Was it working just by chance and returning 0 before?
>
> Probably yes.

(gdb) info symbol &lcore_config[-1].core_id
vfio_cfgs + 444820 in section .bss of
/home/dmarchan/git/pub/dpdk.org/build/app/../lib/librte_eal.so.20.0

Please, update the commitlog.
Thanks.


-- 
David Marchand