From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by inbox.dpdk.org (Postfix) with ESMTP id 1EA9E46AE5; Thu, 3 Jul 2025 19:29:34 +0200 (CEST) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id CFFB540267; Thu, 3 Jul 2025 19:29:33 +0200 (CEST) Received: from dkmailrelay1.smartsharesystems.com (smartserver.smartsharesystems.com [77.243.40.215]) by mails.dpdk.org (Postfix) with ESMTP id F3B6540264 for ; Thu, 3 Jul 2025 19:29:32 +0200 (CEST) Received: from smartserver.smartsharesystems.com (smartserver.smartsharesys.local [192.168.4.10]) by dkmailrelay1.smartsharesystems.com (Postfix) with ESMTP id BEA3220636; Thu, 3 Jul 2025 19:29:32 +0200 (CEST) Content-class: urn:content-classes:message Subject: RE: [RFC] ethdev: TX mbuf fast release optimization MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Date: Thu, 3 Jul 2025 19:29:30 +0200 X-MimeOLE: Produced By Microsoft Exchange V6.5 Message-ID: <98CBD80474FA8B44BF855DF32C47DC35E9FD8A@smartserver.smartshare.dk> In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [RFC] ethdev: TX mbuf fast release optimization Thread-Index: AdvsMCkuXmSA/EajSdSuzZP5LNiQdgADnmrw References: <98CBD80474FA8B44BF855DF32C47DC35E9FD87@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35E9FD88@smartserver.smartshare.dk> <98CBD80474FA8B44BF855DF32C47DC35E9FD89@smartserver.smartshare.dk> From: =?iso-8859-1?Q?Morten_Br=F8rup?= To: "Bruce Richardson" Cc: , "Konstantin Ananyev" , X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > Sent: Thursday, 3 July 2025 17.36 >=20 > On Thu, Jul 03, 2025 at 05:29:26PM +0200, Morten Br=F8rup wrote: > > > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > > > Sent: Thursday, 3 July 2025 17.21 > > > > > > On Thu, Jul 03, 2025 at 05:12:46PM +0200, Morten Br=F8rup wrote: > > > > > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > > > > > Sent: Thursday, 3 July 2025 16.14 > > > > > > > > > > On Thu, Jul 03, 2025 at 03:59:14PM +0200, Morten Br=F8rup = wrote: > > > > > > For TX mbuf fast release offload, I propose to add the mbuf > > > mempool > > > > > > pointer to the ethdev tx queue configuration structure, > > > > > > so the ethdev TX burst operation doesn't need to fetch it = from > the > > > > > > first mbuf of each burst being fast free'd to the mempool. > > > > > > > > > > > > This modification of the struct rte_eth_txconf, and the > > > requirement > > > > > > to set the mempool pointer if the > > > RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE > > > > > > flag is set, will be an API+ABI change in 25.11. > > > > > > Should it be announced in the 25.07 release notes? > > > > > > > > > > > > Note: We could phase it in softly by letting the ethdev > drivers > > > > > > check if the pointer has been set, and fall back to fetching > it > > > > > > from mbuf[0] if not. > > > > > > > > > > > > /** > > > > > > * A structure used to configure a Tx ring of an Ethernet > port. > > > > > > */ > > > > > > struct rte_eth_txconf { > > > > > > struct rte_eth_thresh tx_thresh; /**< Tx ring threshold > > > registers. > > > > > */ > > > > > > uint16_t tx_rs_thresh; /**< Drives the setting of RS bit on > > > TXDs. > > > > > */ > > > > > > uint16_t tx_free_thresh; /**< Start freeing Tx buffers if > > > there > > > > > are > > > > > > less free descriptors than this > > > value. */ > > > > > > > > > > > > uint8_t tx_deferred_start; /**< Do not start queue with > > > > > rte_eth_dev_start(). */ > > > > > > /** > > > > > > * Per-queue Tx offloads to be set using > > > RTE_ETH_TX_OFFLOAD_* > > > > > flags. > > > > > > * Only offloads set on tx_queue_offload_capa or > > > tx_offload_capa > > > > > > * fields on rte_eth_dev_info structure are allowed to be > > > set. > > > > > > */ > > > > > > uint64_t offloads; > > > > > > > > > > > > + /** > > > > > > + * Per-queue mempool to release the mbufs to; required for > > > > > > + * RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE offload. > > > > > > + */ > > > > > > + struct rte_mempool *mp; > > > > > > + > > > > > > > > > > Is this really best put in the txconf struct? Would it not be > better > > > > > just > > > > > stored in the queue structure on free or Tx of the first = packet? > > > That > > > > > would > > > > > make it not change the ABI. > > > > > > > > It seems natural to me to specify the mempool at configuration > time, > > > > because it is a configuration parameter. > > > > The txconf struct seemed like the best place to put it. > > > > > > > > Fetching it from the first mbuf of each burst at runtime, and > possibly > > > caching it, seems like a workaround for the missing configuration > > > parameter. > > > > > > > Not suggesting from each burst, just the first mbuf seen. One time > only. > > > > That's what I meant by "possibly caching it". :-) > > > > The check for the one-time cache update still takes up code space in > the per-burst fast path. (Although very little.) > > > > But I still prefer providing configuration information at > configuration time, rather than snooping it at runtime. > > > Ok, but then are we mandating that all existing apps now are required = to > pass in a mempool value on Tx queue config? I'm concerned about how = many > apps that may affect. On the other hand, if it is optional, does that > not > slow down the fastpath more having to check for this optional value? Initially, it will be optional, and log a warning if not provided. And yes, the fast path will incur a performance cost for checking its = presence. When its "experimental" status expires, it will be required, and return = failure if not provided. Then the fast path no longer needs to consider its non-presence, and the = performance cost can be eliminated.