From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olivier Matz Subject: Re: Adding API to force freeing consumed buffers in TX ring Date: Mon, 21 Nov 2016 16:06:32 +0100 Message-ID: References: <7E8AE555-F016-4F33-B046-A5DA86F493F3@cisco.com> <27853C4C-2482-49E0-8F60-178473276CF5@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: "dev@dpdk.org" To: "Wiles, Keith" , "Damjan Marion (damarion)" Return-path: Received: from mail.droids-corp.org (zoll.droids-corp.org [94.23.50.67]) by dpdk.org (Postfix) with ESMTP id 086276893 for ; Mon, 21 Nov 2016 16:06:38 +0100 (CET) In-Reply-To: <27853C4C-2482-49E0-8F60-178473276CF5@intel.com> List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" Hi, On 11/21/2016 03:33 PM, Wiles, Keith wrote: > >> On Nov 21, 2016, at 4:48 AM, Damjan Marion (damarion) wrote: >> >> >> Hi, >> >> Currently in VPP we do memcpy of whole packet when we need to do >> replication as we cannot know if specific buffer is transmitted >> from tx ring before we update it again (i.e. l2 header rewrite). >> >> Unless there is already a way to address this issue in DPDK which I’m not aware >> of my proposal is that we provide mechanism for polling TX ring >> for consumed buffers. This can be either completely new API or >> extension of rte_etx_tx_burst (i.e. special case when nb_pkts=0). >> >> This will allows us to start polling tx ring when we expect some >> mbuf back, instead of waiting for next tx burst (which we don’t know >> when it will happen) and hoping that we will reach free_threshold soon. > > +1 > > In Pktgen I have the problem of not being able to reclaim all of the TX mbufs to update them for the next set of packets to send. I know this is not a common case, but I do see the case where the application needs its mbufs freed off the TX ring. Currently you need to have at least a TX ring size of mbufs on hand to make sure you can send to a TX ring. If you allocate too few you run into a deadlock case as the number of mbufs on a TX ring does not hit the flush mark. If you are sending to multiple TX rings on the same numa node from the a single TX pool you have to understand the total number of mbufs you need to have allocated to hit the TX flush on each ring. Not a clean way to handle the problems as you may have limited memory or require some logic to add more mbufs for dynamic port s. > > Anyway it would be great to require a way to clean up the TX done ring, using nb_pkts == 0 is the simplest way, but a new API is fine too. >> >> Any thoughts? Yes, it looks useful to have a such API. I would prefer another function instead of diverting the meaning of nb_pkts. Maybe this? void rte_eth_tx_free_bufs(uint8_t port_id, uint16_t queue_id); Regards, Olivier