[PATCH v5 0/3] Recycle buffers from Tx to Rx

[Ferruh Yigit]

On 3/30/2023 7:29 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 buffer
> recycle mode.
> 
> In the latest version, buffer 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: rxq_buf_recycle_info = rte_eth_rx_buf_recycle_info_get(rx_portid, rx_queueid)
> Step 3: rte_eth_dev_buf_recycle(rx_portid, rx_queueid, tx_portid, tx_queueid, rxq_buf_recycle_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 runtime and user does not need to
> know the direction of flow in advance. This can effectively expand buffer recycle mode's
> use scenarios.
> 
> Furthermore, buffer recycle mode is no longer limited to the same pmd,
> it can support moving buffers between different vendor pmds, even can put the buffer
> anywhere into your Rx buffer ring as long as the address of the buffer ring can be provided.
> In the latest version, we enable direct-rearm 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 buffer recycle mode.
> 
> Difference between buffer 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 buffer 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, buffer recycle reduce 32+32=64 pkts memcpy;
> Compared to ZC API used in mempool, we can see buffer recycle reduce 32 pkts memcpy in each loop.
> So, buffer 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%
> -------------------------------------------------------------
> 

Thanks for the perf test reports.

Since test is done on Intel NICs, it would be great to get some testing
and performance numbers from Intel side too, if possible.

> 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
> 
> Feifei Wang (3):
>   ethdev: add API for buffer recycle mode
>   net/i40e: implement recycle buffer mode
>   net/ixgbe: implement recycle buffer mode
> 
>  drivers/net/i40e/i40e_ethdev.c   |   1 +
>  drivers/net/i40e/i40e_ethdev.h   |   2 +
>  drivers/net/i40e/i40e_rxtx.c     | 159 +++++++++++++++++++++
>  drivers/net/i40e/i40e_rxtx.h     |   4 +
>  drivers/net/ixgbe/ixgbe_ethdev.c |   1 +
>  drivers/net/ixgbe/ixgbe_ethdev.h |   3 +
>  drivers/net/ixgbe/ixgbe_rxtx.c   | 153 ++++++++++++++++++++
>  drivers/net/ixgbe/ixgbe_rxtx.h   |   4 +
>  lib/ethdev/ethdev_driver.h       |  10 ++
>  lib/ethdev/ethdev_private.c      |   2 +
>  lib/ethdev/rte_ethdev.c          |  33 +++++
>  lib/ethdev/rte_ethdev.h          | 230 +++++++++++++++++++++++++++++++
>  lib/ethdev/rte_ethdev_core.h     |  15 +-
>  lib/ethdev/version.map           |   6 +
>  14 files changed, 621 insertions(+), 2 deletions(-)
> 

Is usage sample of these new APIs planned? Can it be a new forwarding
mode in testpmd?