回复: [PATCH 1/2] net/i40e: replace put function

[Feifei Wang <Feifei.Wang2@arm.com>]

Hi, Morten

> -----邮件原件-----
> 发件人: Morten Brørup <mb@smartsharesystems.com>
> 发送时间: Thursday, February 9, 2023 5:34 PM
> 收件人: Kamalakshitha Aligeri <Kamalakshitha.Aligeri@arm.com>;
> Yuying.Zhang@intel.com; beilei.xing@intel.com; olivier.matz@6wind.com;
> andrew.rybchenko@oktetlabs.ru; bruce.richardson@intel.com;
> konstantin.ananyev@huawei.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>
> 抄送: dev@dpdk.org; nd <nd@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Feifei Wang <Feifei.Wang2@arm.com>
> 主题: RE: [PATCH 1/2] net/i40e: replace put function
> 
> > From: Kamalakshitha Aligeri [mailto:kamalakshitha.aligeri@arm.com]
> > Sent: Thursday, 9 February 2023 07.25
> >
> > Integrated zero-copy put API in mempool cache in i40e PMD.
> > On Ampere Altra server, l3fwd single core's performance improves by 5%
> > with the new API
> >
> > Signed-off-by: Kamalakshitha Aligeri <kamalakshitha.aligeri@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > Reviewed-by: Feifei Wang <feifei.wang2@arm.com>
> > ---
> > Link:
> > https://patchwork.dpdk.org/project/dpdk/patch/20221227151700.80887-1-
> > mb@smartsharesystems.com/
> >
> >  .mailmap                                |  1 +
> >  drivers/net/i40e/i40e_rxtx_vec_common.h | 34
> > ++++++++++++++++++++-----
> >  2 files changed, 28 insertions(+), 7 deletions(-)
> >
> > diff --git a/.mailmap b/.mailmap
> > index 75884b6fe2..05a42edbcf 100644
> > --- a/.mailmap
> > +++ b/.mailmap
> > @@ -670,6 +670,7 @@ Kai Ji <kai.ji@intel.com>  Kaiwen Deng
> > <kaiwenx.deng@intel.com>  Kalesh AP
> > <kalesh-anakkur.purayil@broadcom.com>
> >  Kamalakannan R <kamalakannan.r@intel.com>
> > +Kamalakshitha Aligeri <kamalakshitha.aligeri@arm.com>
> >  Kamil Bednarczyk <kamil.bednarczyk@intel.com>  Kamil Chalupnik
> > <kamilx.chalupnik@intel.com>  Kamil Rytarowski
> > <kamil.rytarowski@caviumnetworks.com>
> > diff --git a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > index fe1a6ec75e..80d4a159e6 100644
> > --- a/drivers/net/i40e/i40e_rxtx_vec_common.h
> > +++ b/drivers/net/i40e/i40e_rxtx_vec_common.h
> > @@ -95,17 +95,37 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)
> >
> >  	n = txq->tx_rs_thresh;
> >
> > -	 /* first buffer to free from S/W ring is at index
> > -	  * tx_next_dd - (tx_rs_thresh-1)
> > -	  */
> > +	/* first buffer to free from S/W ring is at index
> > +	 * tx_next_dd - (tx_rs_thresh-1)
> > +	 */
> >  	txep = &txq->sw_ring[txq->tx_next_dd - (n - 1)];
> >
> >  	if (txq->offloads & RTE_ETH_TX_OFFLOAD_MBUF_FAST_FREE) {
> > -		for (i = 0; i < n; i++) {
> > -			free[i] = txep[i].mbuf;
> > -			/* no need to reset txep[i].mbuf in vector path */
> > +		struct rte_mempool *mp = txep[0].mbuf->pool;
> > +		struct rte_mempool_cache *cache =
> > rte_mempool_default_cache(mp, rte_lcore_id());
> > +
> > +		if (!cache || n > RTE_MEMPOOL_CACHE_MAX_SIZE) {
> 
> If the mempool has a cache, do not compare n to
> RTE_MEMPOOL_CACHE_MAX_SIZE. Instead, call
> rte_mempool_cache_zc_put_bulk() to determine if n is acceptable for zero-
> copy.
> 

> It looks like this patch behaves incorrectly if the cache is configured to be
> smaller than RTE_MEMPOOL_CACHE_MAX_SIZE. Let's say the cache size is 8,
> which will make the flush threshold 12. If n is 32, your code will not enter this
> branch, but proceed to call rte_mempool_cache_zc_put_bulk(), which will
> return NULL, and then you will goto done.
> 
> Obviously, if there is no cache, fall back to the standard
> rte_mempool_put_bulk().

Agree with this. I think we ignore the case that (cache -> flushthresh  < n <  RTE_MEMPOOL_CACHE_MAX_SIZE).

Our goal is that if (!cache || n > cache -> flushthresh), we can put the buffers
into mempool directly.  

Thus maybe we can change as:
struct rte_mempool_cache *cache = rte_mempool_default_cache(mp, rte_lcore_id());
if (!cache || n > cache -> flushthresh) {
      for (i = 0; i < n ; i++)
          free[i] = txep[i].mbuf;
      if (!cache) {
                rte_mempool_generic_put;
                goto done;
      } else if {
                rte_mempool_ops_enqueue_bulk;
                goto done;
      }
}

If we can change like this?

> 
> > +			for (i = 0; i < n ; i++)
> > +				free[i] = txep[i].mbuf;
> > +			if (!cache) {
> > +				rte_mempool_generic_put(mp, (void
> **)free, n,
> > cache);
> > +				goto done;
> > +			}
> > +			if (n > RTE_MEMPOOL_CACHE_MAX_SIZE) {
> > +				rte_mempool_ops_enqueue_bulk(mp, (void
> **)free,
> > n);
> > +				goto done;
> > +			}
> > +		}
> > +		void **cache_objs;
> > +
> > +		cache_objs = rte_mempool_cache_zc_put_bulk(cache, mp,
> n);
> > +		if (cache_objs) {
> > +			for (i = 0; i < n; i++) {
> > +				cache_objs[i] = txep->mbuf;
> > +				/* no need to reset txep[i].mbuf in vector
> path
> > */
> > +				txep++;
> > +			}
> >  		}
> > -		rte_mempool_put_bulk(free[0]->pool, (void **)free, n);
> >  		goto done;
> >  	}
> >
> > --
> > 2.25.1
> >