Re: [PATCH] doc/eal: add caveat about spinlocks from non-pinned threads

[Stephen Hemminger <stephen@networkplumber.org>]

On Sat, 11 Jun 2022 09:55:00 +0800
fengchengwen <fengchengwen@huawei.com> wrote:

> On 2022/6/10 23:28, Stephen Hemminger wrote:
> > Need to warn users of DPDK spinlocks from non-pinned threads.
> > This is similar wording to Linux documentation in pthread_spin_init.
> > 
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> >  doc/guides/prog_guide/env_abstraction_layer.rst | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
> > index 5f0748fba1c0..45d3de8d84f6 100644
> > --- a/doc/guides/prog_guide/env_abstraction_layer.rst
> > +++ b/doc/guides/prog_guide/env_abstraction_layer.rst
> > @@ -797,6 +797,16 @@ Known Issues
> >  
> >    The debug statistics of rte_ring, rte_mempool and rte_timer are not supported in an unregistered non-EAL pthread.
> >  
> > ++ locking
> > +
> > +  If a pthread, that is not pinned to an lcore acquires a lock such as a
> > +  DPDK based lock (rte_spinlock, rte_rwlock, rte_ticketlock, rte_mcslock)  
> 
> Some APIs inherently use rte_spinlock, just like rte_malloc/rte_eal_alarm_set,
> Because DPDK API mainly use rte_spinlock to support thread-safty.
> 
> Suggest declare DPDK API mainly use rte_spinlock to support thread-safty, so
> if the caller thread is not pinned to an lcore may encount a possibility of
> large application delays.

I copied text from pthread_spinlock man page. The same caveats apply to
pthread_spinlocks as DPDK; therefore using same wording seemed appropriate.

But it is worth mentioning that other API's may depend on spinlocks internally.