Re: [dpdk-dev] [PATCH v1 1/2] net/i40e: improve performance for scalar Tx

["Xing, Beilei" <beilei.xing@intel.com>]

> -----Original Message-----
> From: Feifei Wang <Feifei.Wang2@arm.com>
> Sent: Friday, June 25, 2021 5:40 PM
> To: Xing, Beilei <beilei.xing@intel.com>
> Cc: dev@dpdk.org; nd <nd@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; nd <nd@arm.com>; nd <nd@arm.com>
> Subject: 回复: [PATCH v1 1/2] net/i40e: improve performance for scalar Tx
> 
> <snip>
> 
> > > int n = txq->tx_rs_thresh;
> > >  int32_t i = 0, j = 0;
> > > const int32_t k = RTE_ALIGN_FLOOR(n, RTE_I40E_TX_MAX_FREE_BUF_SZ);
> > > const int32_t m = n % RTE_I40E_TX_MAX_FREE_BUF_SZ; struct rte_mbuf
> > > *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];
> > >
> > > For FAST_FREE_MODE:
> > >
> > > if (k) {
> > >  	for (j = 0; j != k - RTE_I40E_TX_MAX_FREE_BUF_SZ;
> > >  			j += RTE_I40E_TX_MAX_FREE_BUF_SZ) {
> > > 		for (i = 0; i <RTE_I40E_TX_MAX_FREE_BUF_SZ; ++i, ++txep) {
> > > 			free[i] = txep->mbuf;
> > > 			txep->mbuf = NULL;
> > > 		}
> > >  		rte_mempool_put_bulk(free[0]->pool, (void **)free,
> > >  					RTE_I40E_TX_MAX_FREE_BUF_SZ);
> > >  	}
> > >  }
> > >
> > > if (m) {
> > >  	for (i = 0; i < m; ++i, ++txep) {
> > > 		free[i] = txep->mbuf;
> > >  		txep->mbuf = NULL;
> > > 	}
> > >  }
> > >  rte_mempool_put_bulk(free[0]->pool, (void **)free, m); }
> 
> > Seems no logical problem, but the code looks heavy due to for loops.
> > Did you run performance with this change when tx_rs_thresh >
> > RTE_I40E_TX_MAX_FREE_BUF_SZ?
> 
> Sorry for my late rely. It takes me some time to do the test for this path and
> following is my test results:
> 
> First, I come up with another way to solve this bug and compare it with
> "loop"(size of 'free' is 64).
> That is set the size of 'free' as a large constant. We know:
> tx_rs_thresh < ring_desc_size < I40E_MAX_RING_DESC(4096), so we can
> directly define as:
> struct rte_mbuf *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];
> 
> [1]Test Config:
> MRR Test: two porst & bi-directional flows & one core RX API:
> i40e_recv_pkts_bulk_alloc TX API: i40e_xmit_pkts_simple
> ring_descs_size: 1024
> Ring_I40E_TX_MAX_FREE_SZ: 64
> 
> [2]Scheme:
> tx_rs_thresh =  I40E_DEFAULT_TX_RSBIT_THRESH tx_free_thresh =
> I40E_DEFAULT_TX_FREE_THRESH tx_rs_thresh <= tx_free_thresh <
> nb_tx_desc So we change the value of 'tx_rs_thresh' by adjust
> I40E_DEFAULT_TX_RSBIT_THRESH
> 
> [3]Test Results (performance improve):
> In X86:
> tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
> 1.mempool_put(base)                                   0                  0                        0
> 2.mempool_put_bulk:loop                           +4.7%         +5.6%               +7.0%
> 3.mempool_put_bulk:large size for free   +3.8%          +2.3%               -2.0%
> (free[I40E_MAX_RING_DESC])
> 
> In Arm:
> N1SDP:
> tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
> 1.mempool_put(base)                                   0                  0                        0
> 2.mempool_put_bulk:loop                           +7.9%         +9.1%               +2.9%
> 3.mempool_put_bulk:large size for free    +7.1%         +8.7%               +3.4%
> (free[I40E_MAX_RING_DESC])
> 
> Thunderx2:
> tx_rs_thresh/ tx_free_thresh                       32/32          256/256          512/512
> 1.mempool_put(base)                                   0                  0                        0
> 2.mempool_put_bulk:loop                           +7.6%         +10.5%             +7.6%
> 3.mempool_put_bulk:large size for free    +1.7%         +18.4%             +10.2%
> (free[I40E_MAX_RING_DESC])
> 
> As a result, I feel maybe 'loop' is better and it seems not very heavy
> according to the test.
> What about your views and look forward to your reply.
> Thanks a lot.

Thanks for your patch and test.
It looks OK for me, please send V2.