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

[Feifei Wang]

Hi, Beilei

Thanks for your comments, please see below.

> -----邮件原件-----
> 发件人: Xing, Beilei <beilei.xing at intel.com>
> 发送时间: 2021年6月22日 14:08
> 收件人: Feifei Wang <Feifei.Wang2 at arm.com>
> 抄送: dev at dpdk.org; nd <nd at arm.com>; Ruifeng Wang
> <Ruifeng.Wang at arm.com>
> 主题: RE: [PATCH v1 1/2] net/i40e: improve performance for scalar Tx
> 
> 
> 
> > -----Original Message-----
> > From: Feifei Wang <feifei.wang2 at arm.com>
> > Sent: Thursday, May 27, 2021 4:17 PM
> > To: Xing, Beilei <beilei.xing at intel.com>
> > Cc: dev at dpdk.org; nd at arm.com; Feifei Wang <feifei.wang2 at arm.com>;
> > Ruifeng Wang <ruifeng.wang at arm.com>
> > Subject: [PATCH v1 1/2] net/i40e: improve performance for scalar Tx
> >
> > For i40e scalar Tx path, if implement FAST_FREE_MBUF mode, it means
> > per- queue all mbufs come from the same mempool and have refcnt = 1.
> >
> > Thus we can use bulk free of the buffers when mbuf fast free mode is
> > enabled.
> >
> > For scalar path in arm platform:
> > In n1sdp, performance is improved by 7.8%; In thunderx2, performance
> > is improved by 6.7%.
> >
> > For scalar path in x86 platform,
> > performance is improved by 6%.
> >
> > Suggested-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > Signed-off-by: Feifei Wang <feifei.wang2 at arm.com>
> > ---
> >  drivers/net/i40e/i40e_rxtx.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > b/drivers/net/i40e/i40e_rxtx.c index
> > 6c58decece..fe7b20f750 100644
> > --- a/drivers/net/i40e/i40e_rxtx.c
> > +++ b/drivers/net/i40e/i40e_rxtx.c
> > @@ -1295,6 +1295,7 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)  {
> >  	struct i40e_tx_entry *txep;
> >  	uint16_t i;
> > +	struct rte_mbuf *free[RTE_I40E_TX_MAX_FREE_BUF_SZ];
> >
> >  	if ((txq->tx_ring[txq->tx_next_dd].cmd_type_offset_bsz &
> >
> 	rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) != @@ -1308,9
> +1309,11
> > @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)
> >
> >  	if (txq->offloads & DEV_TX_OFFLOAD_MBUF_FAST_FREE) {
> >  		for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
> > -			rte_mempool_put(txep->mbuf->pool, txep->mbuf);
> > +			free[i] = txep->mbuf;
> 
> The tx_rs_thresh can be 'nb_desc - 3', so if tx_rs_thres >
> RTE_I40E_TX_MAX_FREE_BUF_SZ, there'll be out of bounds, right?

Actually tx_rs_thresh  <=  tx__free_thresh  <  nb_desc - 3 (i40e_dev_tx_queue_setup).
However, I don't know how it affects the relationship between tx_rs_thresh and
RTE_I40E_TX_MAX_FREE_BUF_SZ.

Furthermore, I think you are right that tx_rs_thres can be greater than
RTE_I40E_TX_MAX_FREE_BUF_SZ in tx_simple_mode (i40e_set_tx_function_flag).

Thus, in scalar path, we can change like:
---------------------------------------------------------------------------------------------------------------
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);
	}
} else {
	for (i = 0; i < m; ++i, ++txep) {
		free[i] = txep->mbuf;
		txep->mbuf = NULL;
	}
	rte_mempool_put_bulk(free[0]->pool, (void **)free, m);
}
---------------------------------------------------------------------------------------------------------------

Best Regards
Feifei