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

[fengchengwen]

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 at 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.

> +  then there is a possibility of large application delays.
> +  The problem is that if a thread is scheduled off the CPU while it holds
> +  a lock, then other threads will waste time spinning on the lock until
> +  the lock holder is once more rescheduled and releases the lock.
> +
> +
>  cgroup control
>  ~~~~~~~~~~~~~~
>  
>