RE: [PATCH v3 0/3] Direct re-arming of buffers on receive side

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> -----Original Message-----
> From: Morten Brørup <mb@smartsharesystems.com>
> Sent: Wednesday, March 22, 2023 7:57 AM
> To: Feifei Wang <Feifei.Wang2@arm.com>
> Cc: dev@dpdk.org; konstantin.v.ananyev@yandex.ru; nd <nd@arm.com>;
> konstantin.ananyev@huawei.com; Yuying Zhang <Yuying.Zhang@intel.com>;
> Beilei Xing <beilei.xing@intel.com>; Ruifeng Wang <Ruifeng.Wang@arm.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Subject: RE: [PATCH v3 0/3] Direct re-arming of buffers on receive side
> 
> > From: Feifei Wang [mailto:feifei.wang2@arm.com]
> > Sent: Wednesday, 4 January 2023 08.31
> >
> > 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.
> 
> I am starting to wonder if we have been adding unnecessary feature creep in
> order to make this feature too generic.
Can you please elaborate on the feature creep you are thinking? The features have been the same since the first implementation, but it is made more generic.

> 
> Could you please describe some of the most important high-volume use cases
> from real life? It would help setting the scope correctly.
The use cases have been discussed several times already.

> 
> >
> > However, this solution poses several constraints:
> >
> > 1)The receive queue needs to know which transmit queue it should take
> > the buffers from. The application logic decides which transmit port to
> > use to send out the packets. In many use cases the NIC might have a
> > single port ([1], [2], [3]), in which case a given transmit queue is
> > always mapped to a single receive queue (1:1 Rx queue: Tx queue). This
> > is easy to configure.
> >
> > If the NIC has 2 ports (there are several references), then we will
> > have
> > 1:2 (RX queue: TX queue) mapping which is still easy to configure.
> > However, if this is generalized to 'N' ports, the configuration can be
> > long. More over the PMD would have to scan a list of transmit queues
> > to pull the buffers from.
> >
> > 2)The other factor that needs to be considered is 'run-to-completion'
> > vs 'pipeline' models. In the run-to-completion model, the receive side
> > and the transmit side are running on the same lcore serially. In the
> > pipeline model. The receive side and transmit side might be running on
> > different lcores in parallel. This requires locking. This is not
> > supported at this point.
> >
> > 3)Tx and Rx buffers must be from the same mempool. And we also must
> > ensure Tx buffer free number is equal to Rx buffer free number.
> > Thus, 'tx_next_dd' can be updated correctly in direct-rearm mode. This
> > is due to tx_next_dd is a variable to compute tx sw-ring free location.
> > Its value will be one more round than the position where next time
> > free starts.
> >
> > Current status in this patch:
> > 1)Two APIs are added for users to enable direct-rearm mode:
> >   In control plane, users can call 'rte_eth_rx_queue_rearm_data_get'
> >   to get Rx sw_ring pointer and its rxq_info.
> >   (This avoid Tx load Rx data directly);
> >
> >   In data plane, users can  call 'rte_eth_dev_direct_rearm' to rearm Rx
> >   buffers and free Tx buffers at the same time. Specifically, in this
> >   API, there are two separated API for Rx and Tx.
> >   For Tx, 'rte_eth_tx_fill_sw_ring' can fill a given sw_ring by Tx
> > freed buffers.
> >   For Rx, 'rte_eth_rx_flush_descriptor' can flush its descriptors based
> >   on the rearm buffers.
> >   Thus, this can separate Rx and Tx operation, and user can even re-arm
> >   RX queue not from the same driver's TX queue, but from different
> >   sources too.
> > -----------------------------------------------------------------------
> >   control plane:
> >   	rte_eth_rx_queue_rearm_data_get(*rxq_rearm_data);
> >   data plane:
> >   	loop {
> >   		rte_eth_dev_direct_rearm(*rxq_rearm_data){
> >
> > 			rte_eth_tx_fill_sw_ring{
> >      				for (i = 0; i <= 32; i++) {
> >        					sw_ring.mbuf[i] = tx.mbuf[i];
> > 				}
> >     			}
> >
> > 			rte_eth_rx_flush_descriptor{
> > 				for (i = 0; i <= 32; i++) {
> > 					flush descs[i];
> > 				}
> > 			}
> > 		}
> > 		rte_eth_rx_burst;
> > 		rte_eth_tx_burst;
> >   	}
> > ----------------------------------------------------------------------
> > - 2)The i40e driver is changed to do the direct re-arm of the receive
> >   side.
> > 3)The ixgbe driver is changed to do the direct re-arm of the receive
> >   side.
> >
> > Testing status:
> > (1) dpdk l3fwd test with multiple drivers:
> >     port 0: 82599 NIC   port 1: XL710 NIC
> > -------------------------------------------------------------
> > 		Without fast free	With fast free
> > Thunderx2:      +9.44%	                +7.14%
> > -------------------------------------------------------------
> >
> > (2) dpdk l3fwd test with same driver:
> >     port 0 && 1: XL710 NIC
> > -------------------------------------------------------------
> > *Direct rearm with exposing rx_sw_ring:
> > 		Without fast free	With fast free
> > Ampere altra:   +14.98%		        +15.77%
> > n1sdp:		+6.47%			+0.52%
> > -------------------------------------------------------------
> >
> > (3) VPP test with same driver:
> >     port 0 && 1: XL710 NIC
> > -------------------------------------------------------------
> > *Direct rearm with exposing rx_sw_ring:
> > Ampere altra:     +4.59%
> > n1sdp:		  +5.4%
> > -------------------------------------------------------------
> >
> > Reference:
> > [1]
> > https://store.nvidia.com/en-us/networking/store/product/MCX623105AN-
> >
> CDAT/NVIDIAMCX623105ANCDATConnectX6DxENAdapterCard100GbECrypto
> Disabled
> > / [2]
> > https://www.intel.com/content/www/us/en/products/sku/192561/intel-
> > ethernet-network-adapter-e810cqda1/specifications.html
> > [3] https://www.broadcom.com/products/ethernet-connectivity/network-
> > adapters/100gb-nic-ocp/n1100g
> >
> > 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
> >
> > Feifei Wang (3):
> >   ethdev: enable direct rearm with separate API
> >   net/i40e: enable direct rearm with separate API
> >   net/ixgbe: enable direct rearm with separate API
> >
> >  drivers/net/i40e/i40e_ethdev.c            |   1 +
> >  drivers/net/i40e/i40e_ethdev.h            |   2 +
> >  drivers/net/i40e/i40e_rxtx.c              |  19 +++
> >  drivers/net/i40e/i40e_rxtx.h              |   4 +
> >  drivers/net/i40e/i40e_rxtx_vec_common.h   |  54 +++++++
> >  drivers/net/i40e/i40e_rxtx_vec_neon.c     |  42 ++++++
> >  drivers/net/ixgbe/ixgbe_ethdev.c          |   1 +
> >  drivers/net/ixgbe/ixgbe_ethdev.h          |   3 +
> >  drivers/net/ixgbe/ixgbe_rxtx.c            |  19 +++
> >  drivers/net/ixgbe/ixgbe_rxtx.h            |   4 +
> >  drivers/net/ixgbe/ixgbe_rxtx_vec_common.h |  48 ++++++
> >  drivers/net/ixgbe/ixgbe_rxtx_vec_neon.c   |  52 +++++++
> >  lib/ethdev/ethdev_driver.h                |  10 ++
> >  lib/ethdev/ethdev_private.c               |   2 +
> >  lib/ethdev/rte_ethdev.c                   |  52 +++++++
> >  lib/ethdev/rte_ethdev.h                   | 174 ++++++++++++++++++++++
> >  lib/ethdev/rte_ethdev_core.h              |  11 ++
> >  lib/ethdev/version.map                    |   6 +
> >  18 files changed, 504 insertions(+)
> >
> > --
> > 2.25.1
> >