Re: [dpdk-dev] [RFC] ethdev: make rte flow API thread safe

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu,  3 Sep 2020 12:53:02 +0800
Suanming Mou <suanmingm@nvidia.com> wrote:

> Currently, the rte flow functions are not defined as thread safety.
> DPDK applications either call the functions in single thread or add
> locks around the functions for the critical section.
> 
> For PMDs support the flow operations thread safe natively, the
> redundant protection in application hurts the performance of the
> rte flow operation functions.
> 
> And the restriction of thread safety not guaranteed for the rte
> flow functions also limits the applications' expectation.
> 
> This feature is going to change the rte flow functions to be thread
> safety. As different PMDs have different flow operations, some may
> support thread safety already and others may not. For PMDs don't
> support flow thread safe operation, a new lock is defined in ethdev
> in order to protects thread unsafe PMDs from rte flow level.
> 
> A new RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE device flag is added to
> determine whether the PMD supports thread safe flow operation or not.
> For PMDs support thread safe flow operations, set the
> RTE_ETH_DEV_FLOW_OPS_THREAD_SAFE flag, rte flow level functions will
> skip the thread safe helper lock for these PMDs. Again the rte flow
> level thread safe lock only works when PMD operation functions are
> not thread safety.
> 
> The change has no effect on the current DPDK applications. No change
> is required for the current DPDK applications.
> 
> Signed-off-by: Suanming Mou <suanmingm@nvidia.com>

What is the performance impact of this for currently working applications
that use a single thread to program flow rules.  You are adding a couple of
system calls to what was formerly a totally usermode operation.