From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olivier Matz Subject: Re: [PATCH v6 1/3] ethdev: new API to free consumed buffers in Tx ring Date: Wed, 15 Mar 2017 11:29:08 +0100 Message-ID: <20170315112908.15b4c811@platinum> References: <20170127183800.27466-1-bmcfall@redhat.com> <20170309205119.28170-1-bmcfall@redhat.com> <20170309205119.28170-2-bmcfall@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: thomas.monjalon@6wind.com, wenzhuo.lu@intel.com, dev@dpdk.org To: Billy McFall Return-path: Received: from mail-wr0-f170.google.com (mail-wr0-f170.google.com [209.85.128.170]) by dpdk.org (Postfix) with ESMTP id 21B0E1396 for ; Wed, 15 Mar 2017 11:29:11 +0100 (CET) Received: by mail-wr0-f170.google.com with SMTP id u108so7820990wrb.3 for ; Wed, 15 Mar 2017 03:29:11 -0700 (PDT) In-Reply-To: <20170309205119.28170-2-bmcfall@redhat.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi Billy, On Thu, 9 Mar 2017 15:51:17 -0500, Billy McFall 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 [...] > 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). Thanks, Olivier