Re: [PATCH v6 1/3] ethdev: new API to free consumed buffers in Tx ring

[Billy McFall <bmcfall@redhat.com>]

On Wed, Mar 15, 2017 at 6:29 AM, Olivier Matz <olivier.matz@6wind.com>
wrote:

> Hi Billy,
>
> On Thu,  9 Mar 2017 15:51:17 -0500, Billy McFall <bmcfall@redhat.com>
> wrote:
> > Add a new API to force free consumed buffers on Tx ring. API will return
> > the number of packets freed (0-n) or error code if feature not supported
> > (-ENOTSUP) or input invalid (-ENODEV).
> >
> > Please double check my python coding in conf.py and make sure I
> > implemented 'feature_str_len' properly.
> >
> > Signed-off-by: Billy McFall <bmcfall@redhat.com>
>
> [...]
>
> > diff --git a/doc/guides/prog_guide/mempool_lib.rst
> b/doc/guides/prog_guide/mempool_lib.rst
> > index ffdc109..a117881 100644
> > --- a/doc/guides/prog_guide/mempool_lib.rst
> > +++ b/doc/guides/prog_guide/mempool_lib.rst
> > @@ -132,6 +132,32 @@ These user-owned caches can be explicitly passed to
> ``rte_mempool_generic_put()`
> >  The ``rte_mempool_default_cache()`` call returns the default internal
> cache if any.
> >  In contrast to the default caches, user-owned caches can be used by
> non-EAL threads too.
> >
> > +In addition to a core's local cache, many of the drivers don't release
> the mbuf back to the mempool, or local cache,
> > +immediately after the packet has been transmitted.
> > +Instead, they leave the mbuf in their Tx ring and either perform a bulk
> release when the ``tx_rs_thresh`` has been
> > +crossed or free the mbuf when a slot in the Tx ring is needed.
> > +
> > +An application can request the driver to release used mbufs with the
> ``rte_eth_tx_done_cleanup()`` API.
> > +This API requests the driver to release mbufs that are no longer in
> use, independent of whether or not the
> > +``tx_rs_thresh`` has been crossed.
> > +There are two scenarios when an application may want the mbuf released
> immediately:
> > +
> > +* When a given packet needs to be sent to multiple destination
> interfaces (either for Layer 2 flooding or Layer 3
> > +  multi-cast).
> > +  One option is to make a copy of the packet or a copy of the header
> portion that needs to be manipulated.
> > +  A second option is to transmit the packet and then poll the
> ``rte_eth_tx_done_cleanup()`` API until the reference
> > +  count on the packet is decremented.
> > +  Then the same packet can be transmitted to the next destination
> interface.
> > +
> > +* If an application is designed to make multiple runs, like a packet
> generator, and one run has completed.
> > +  The application may want to reset to a clean state.
> > +  In this case, it may want to call the ``rte_eth_tx_done_cleanup()``
> API to request each destination interface it has
> > +  been using to release all of its used mbufs.
> > +
> > +To determine if a driver supports this API, check for the *Free Tx mbuf
> on demand* feature in the *Network Interface
> > +Controller Drivers* document.
>
> I'm not sure the mempool documentation is the proper place to document
> this API. I'll suggest to move it in ethdev documentation
> (poll_mode_drv.rst).
>
> You can keep a small paragraph in mempool lib, but keep in mind that
> mempool is not necessarily a pool of mbuf (it can be any kind of object).
>
> Not sure this API needs to be documented in multiple places. I'll move the
content to the poll_mode_drv.rst file.

>
> Thanks,
> Olivier
>
> Billy