Re: [PATCH v13 0/4] Recycle mbufs from Tx queue into Rx queue

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 9/25/2023 4:19 AM, Feifei Wang wrote:
> Currently, the transmit side frees the buffers into the lcore cache and
> the receive side allocates buffers from the lcore cache. The transmit
> side typically frees 32 buffers resulting in 32*8=256B of stores to
> lcore cache. The receive side allocates 32 buffers and stores them in
> the receive side software ring, resulting in 32*8=256B of stores and
> 256B of load from the lcore cache.
> 
> This patch proposes a mechanism to avoid freeing to/allocating from
> the lcore cache. i.e. the receive side will free the buffers from
> transmit side directly into its software ring. This will avoid the 256B
> of loads and stores introduced by the lcore cache. It also frees up the
> cache lines used by the lcore cache. And we can call this mode as mbufs
> recycle mode.
> 
> In the latest version, mbufs recycle mode is packaged as a separate API. 
> This allows for the users to change rxq/txq pairing in real time in data plane,
> according to the analysis of the packet flow by the application, for example:
> -----------------------------------------------------------------------
> Step 1: upper application analyse the flow direction
> Step 2: recycle_rxq_info = rte_eth_recycle_rx_queue_info_get(rx_portid, rx_queueid)
> Step 3: rte_eth_recycle_mbufs(rx_portid, rx_queueid, tx_portid, tx_queueid, recycle_rxq_info);
> Step 4: rte_eth_rx_burst(rx_portid,rx_queueid);
> Step 5: rte_eth_tx_burst(tx_portid,tx_queueid);
> -----------------------------------------------------------------------
> Above can support user to change rxq/txq pairing  at run-time and user does not need to
> know the direction of flow in advance. This can effectively expand mbufs recycle mode's
> use scenarios.
> 
> Furthermore, mbufs recycle mode is no longer limited to the same pmd,
> it can support moving mbufs between different vendor pmds, even can put the mbufs
> anywhere into your Rx mbuf ring as long as the address of the mbuf ring can be provided.
> In the latest version, we enable mbufs recycle mode in i40e pmd and ixgbe pmd, and also try to
> use i40e driver in Rx, ixgbe driver in Tx, and then achieve 7-9% performance improvement
> by mbufs recycle mode.
> 
> Difference between mbuf recycle, ZC API used in mempool and general path
> For general path: 
>                 Rx: 32 pkts memcpy from mempool cache to rx_sw_ring
>                 Tx: 32 pkts memcpy from tx_sw_ring to temporary variable + 32 pkts memcpy from temporary variable to mempool cache
> For ZC API used in mempool:
>                 Rx: 32 pkts memcpy from mempool cache to rx_sw_ring
>                 Tx: 32 pkts memcpy from tx_sw_ring to zero-copy mempool cache
>                 Refer link: http://patches.dpdk.org/project/dpdk/patch/20230221055205.22984-2-kamalakshitha.aligeri@arm.com/
> For mbufs recycle:
>                 Rx/Tx: 32 pkts memcpy from tx_sw_ring to rx_sw_ring
> Thus we can see in the one loop, compared to general path, mbufs recycle mode reduces 32+32=64 pkts memcpy;
> Compared to ZC API used in mempool, we can see mbufs recycle mode reduce 32 pkts memcpy in each loop.
> So, mbufs recycle has its own benefits.
> 
> Testing status:
> (1) dpdk l3fwd test with multiple drivers:
>     port 0: 82599 NIC   port 1: XL710 NIC
> -------------------------------------------------------------
> 		Without fast free	With fast free
> Thunderx2:      +7.53%	                +13.54%
> -------------------------------------------------------------
> 
> (2) dpdk l3fwd test with same driver:
>     port 0 && 1: XL710 NIC
> -------------------------------------------------------------
> 		Without fast free	With fast free
> Ampere altra:   +12.61%		        +11.42%
> n1sdp:		+8.30%			+3.85%
> x86-sse:	+8.43%			+3.72%
> -------------------------------------------------------------
> 
> (3) Performance comparison with ZC_mempool used
>     port 0 && 1: XL710 NIC
>     with fast free
> -------------------------------------------------------------
> 		With recycle buffer	With zc_mempool
> Ampere altra:	11.42%			3.54%
> -------------------------------------------------------------
> 
> Furthermore, we add recycle_mbuf engine in testpmd. Due to XL710 NIC has
> I/O bottleneck in testpmd in ampere altra, we can not see throughput change
> compared with I/O fwd engine. However, using record cmd in testpmd:
> '$set record-burst-stats on'
> we can see the ratio of 'Rx/Tx burst size of 32' is reduced. This
> indicate mbufs recycle can save CPU cycles.
> 
> V2:
> 1. Use data-plane API to enable direct-rearm (Konstantin, Honnappa)
> 2. Add 'txq_data_get' API to get txq info for Rx (Konstantin)
> 3. Use input parameter to enable direct rearm in l3fwd (Konstantin)
> 4. Add condition detection for direct rearm API (Morten, Andrew Rybchenko)
> 
> V3:
> 1. Seperate Rx and Tx operation with two APIs in direct-rearm (Konstantin)
> 2. Delete L3fwd change for direct rearm (Jerin)
> 3. enable direct rearm in ixgbe driver in Arm
> 
> v4:
> 1. Rename direct-rearm as buffer recycle. Based on this, function name
> and variable name are changed to let this mode more general for all
> drivers. (Konstantin, Morten)
> 2. Add ring wrapping check (Konstantin)
> 
> v5:
> 1. some change for ethdev API (Morten)
> 2. add support for avx2, sse, altivec path
> 
> v6:
> 1. fix ixgbe build issue in ppc
> 2. remove 'recycle_tx_mbufs_reuse' and 'recycle_rx_descriptors_refill'
>    API wrapper (Tech Board meeting)
> 3. add recycle_mbufs engine in testpmd (Tech Board meeting)
> 4. add namespace in the functions related to mbufs recycle(Ferruh)
> 
> v7:
> 1. move 'rxq/txq data' pointers to the beginning of eth_dev structure,
> in order to keep them in the same cache line as rx/tx_burst function
> pointers (Morten)
> 2. add the extra description for 'rte_eth_recycle_mbufs' to show it can
> support feeding 1 Rx queue from 2 Tx queues in the same thread
> (Konstantin)
> 3. For i40e/ixgbe driver, make the previous copied buffers as invalid if
> there are Tx buffers refcnt > 1 or from unexpected mempool (Konstantin)
> 4. add check for the return value of 'rte_eth_recycle_rx_queue_info_get'
> in testpmd fwd engine (Morten)
> 
> v8:
> 1. add arm/x86 build option to fix ixgbe build issue in ppc
> 
> v9:
> 1. delete duplicate file name for ixgbe
> 
> v10:
> 1. fix compile issue on windows
> 
> v11:
> 1. fix doc warning
> 
> v12:
> 1. replace rx queue check code with eth_dev_validate_rx_queue
> function (Stephen)
> 2. put port and queue check before function call (Konstantin)
> 
> v13:
> 1. for i40e and ixgbe drivers, reset nb_recycle_mbufs to zero
> when rxep[i] == NULL, no matter what value refill_requirement
> is (Konstantin)
> 
> Feifei Wang (4):
>   ethdev: add API for mbufs recycle mode
>   net/i40e: implement mbufs recycle mode
>   net/ixgbe: implement mbufs recycle mode
>   app/testpmd: add recycle mbufs engine
> 

Series applied to dpdk-next-net/main, thanks.