Re: [PATCH 6/6] app/testpmd: factorize fwd engine Tx

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 1/24/2023 10:47 AM, David Marchand wrote:
> Reduce code duplication by introducing a helper that takes care of
> transmitting, retrying if enabled and incrementing tx counter.
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>

<...>

> diff --git a/app/test-pmd/noisy_vnf.c b/app/test-pmd/noisy_vnf.c
> index 937d5a1d7d..3875590132 100644
> --- a/app/test-pmd/noisy_vnf.c
> +++ b/app/test-pmd/noisy_vnf.c
> @@ -93,30 +93,6 @@ sim_memory_lookups(struct noisy_config *ncf, uint16_t nb_pkts)
>  	}
>  }
>  
> -static uint16_t
> -do_retry(uint16_t nb_rx, uint16_t nb_tx, struct rte_mbuf **pkts,
> -	 struct fwd_stream *fs)
> -{
> -	uint32_t retry = 0;
> -
> -	while (nb_tx < nb_rx && retry++ < burst_tx_retry_num) {
> -		rte_delay_us(burst_tx_delay_time);
> -		nb_tx += rte_eth_tx_burst(fs->tx_port, fs->tx_queue,
> -				&pkts[nb_tx], nb_rx - nb_tx);
> -	}
> -
> -	return nb_tx;
> -}
> -
> -static uint32_t
> -drop_pkts(struct rte_mbuf **pkts, uint16_t nb_rx, uint16_t nb_tx)
> -{
> -	if (nb_tx < nb_rx)
> -		rte_pktmbuf_free_bulk(&pkts[nb_tx], nb_rx - nb_tx);
> -
> -	return nb_rx - nb_tx;
> -}
> -
>  /*
>   * Forwarding of packets in noisy VNF mode.  Forward packets but perform
>   * memory operations first as specified on cmdline.
> @@ -156,38 +132,23 @@ pkt_burst_noisy_vnf(struct fwd_stream *fs)
>  
>  	if (!ncf->do_buffering) {
>  		sim_memory_lookups(ncf, nb_rx);
> -		nb_tx = rte_eth_tx_burst(fs->tx_port, fs->tx_queue,
> -				pkts_burst, nb_rx);
> -		if (unlikely(nb_tx < nb_rx) && fs->retry_enabled)
> -			nb_tx += do_retry(nb_rx, nb_tx, pkts_burst, fs);
> -		inc_tx_burst_stats(fs, nb_tx);
> -		fs->tx_packets += nb_tx;
> -		fs->fwd_dropped += drop_pkts(pkts_burst, nb_rx, nb_tx);
> +		nb_tx = common_fwd_stream_transmit(fs, pkts_burst, nb_rx);
>  

'nb_tx' is not used or necessary in this context, so assignment is not
necassary.

PS:
In the latest next-net head, there is a 'goto' here instead of return,
but that is becuase of recording cycles, becuase of optimization in this
set (patch 1/6) that needs to turn back to 'return' that is what I did
while applying patch.

>  		kreturn true;
>  	}
>  
>  	fifo_free = rte_ring_free_count(ncf->f);
>  	if (fifo_free >= nb_rx) {
> -		nb_enqd = rte_ring_enqueue_burst(ncf->f,
> -				(void **) pkts_burst, nb_rx, NULL);
> -		if (nb_enqd < nb_rx)
> -			fs->fwd_dropped += drop_pkts(pkts_burst,
> -						     nb_rx, nb_enqd);
> -	} else {
> -		nb_deqd = rte_ring_dequeue_burst(ncf->f,
> -				(void **) tmp_pkts, nb_rx, NULL);
> -		nb_enqd = rte_ring_enqueue_burst(ncf->f,
> -				(void **) pkts_burst, nb_deqd, NULL);
> -		if (nb_deqd > 0) {
> -			nb_tx = rte_eth_tx_burst(fs->tx_port,
> -					fs->tx_queue, tmp_pkts,
> -					nb_deqd);
> -			if (unlikely(nb_tx < nb_rx) && fs->retry_enabled)
> -				nb_tx += do_retry(nb_rx, nb_tx, tmp_pkts, fs);
> -			inc_tx_burst_stats(fs, nb_tx);
> -			fs->fwd_dropped += drop_pkts(tmp_pkts, nb_deqd, nb_tx);
> +		nb_enqd = rte_ring_enqueue_burst(ncf->f, (void **) pkts_burst, nb_rx, NULL);
> +		if (nb_enqd < nb_rx) {
> +			fs->fwd_dropped += nb_rx - nb_enqd;
> +			rte_pktmbuf_free_bulk(&pkts_burst[nb_enqd], nb_rx - nb_enqd);

Why not keep 'drop_pkts()' for this block, it is easier to read with it.

>  		}
> +	} else {
> +		nb_deqd = rte_ring_dequeue_burst(ncf->f, (void **) tmp_pkts, nb_rx, NULL);
> +		nb_enqd = rte_ring_enqueue_burst(ncf->f, (void **) pkts_burst, nb_deqd, NULL);
> +		if (nb_deqd > 0)
> +			nb_tx = common_fwd_stream_transmit(fs, tmp_pkts, nb_deqd);

'nb_tx' assignment looks wrong,
function returns 'nb_dropped' not 'nb_tx'. 'nb_tx' used below to detect
if flush needed ('needs_flush'), so 'needs_flush' may be set wrong
becuase dropped packet is used instead number of Tx packets.

>  	}
>  
>  	sim_memory_lookups(ncf, nb_enqd);
> @@ -204,15 +165,9 @@ pkt_burst_noisy_vnf(struct fwd_stream *fs)
>  	needs_flush = delta_ms >= noisy_tx_sw_buf_flush_time &&
>  			noisy_tx_sw_buf_flush_time > 0 && !nb_tx;
>  	while (needs_flush && !rte_ring_empty(ncf->f)) {
> -		unsigned int sent;
>  		nb_deqd = rte_ring_dequeue_burst(ncf->f, (void **)tmp_pkts,
>  				MAX_PKT_BURST, NULL);
> -		sent = rte_eth_tx_burst(fs->tx_port, fs->tx_queue,
> -					 tmp_pkts, nb_deqd);
> -		if (unlikely(sent < nb_deqd) && fs->retry_enabled)
> -			nb_tx += do_retry(nb_rx, nb_tx, tmp_pkts, fs);
> -		inc_tx_burst_stats(fs, nb_tx);
> -		fs->fwd_dropped += drop_pkts(tmp_pkts, nb_deqd, sent);
> +		nb_tx = common_fwd_stream_transmit(fs, tmp_pkts, nb_deqd);

similaryly 'nb_tx' assignment can be wrong here, and 'nb_tx' used for
return value to hint if record cycle is required, using number of
dropped packets (what 'common_fwd_stream_transmit()' returns) gives
wrong result.

>  		ncf->prev_time = rte_get_timer_cycles();
>  	}
>  
> diff --git a/app/test-pmd/testpmd.h b/app/test-pmd/testpmd.h
> index e6b28b4748..71ff70f55b 100644
> --- a/app/test-pmd/testpmd.h
> +++ b/app/test-pmd/testpmd.h
> @@ -870,6 +870,36 @@ common_fwd_stream_receive(struct fwd_stream *fs, struct rte_mbuf **burst,
>  	return nb_rx;
>  }
>  
> +/* Returns count of dropped packets. */
> +static inline uint16_t
> +common_fwd_stream_transmit(struct fwd_stream *fs, struct rte_mbuf **burst,
> +	unsigned int count)

I would use 'nb_pkts' instead of 'count' as variable name since it is
more common, but of course this is subjective.

> +{
> +	uint16_t nb_tx;
> +	uint32_t retry;
> +
> +	nb_tx = rte_eth_tx_burst(fs->tx_port, fs->tx_queue, burst, count);
> +	/*
> +	 * Retry if necessary
> +	 */
> +	if (unlikely(nb_tx < count) && fs->retry_enabled) {
> +		retry = 0;
> +		while (nb_tx < count && retry++ < burst_tx_retry_num) {
> +			rte_delay_us(burst_tx_delay_time);
> +			nb_tx += rte_eth_tx_burst(fs->tx_port, fs->tx_queue,
> +				&burst[nb_tx], count - nb_tx);
> +		}
> +	}
> +	fs->tx_packets += nb_tx;
> +	inc_tx_burst_stats(fs, nb_tx);
> +	if (unlikely(nb_tx < count)) {
> +		fs->fwd_dropped += (count - nb_tx);
> +		rte_pktmbuf_free_bulk(&burst[nb_tx], count - nb_tx);
> +	}
> +
> +	return count - nb_tx;

Instead of returning number of dropped packets, what about returning
number of packets sent ('nb_tx')?
Intuitively this is what expected from a function named
'common_fwd_stream_transmit()', and even if it is more optimised to
return number of dropped packet, this may have only a little impact on
the caller code.


And even 'fs->tx_packets' updated withing the function, updating it
externally and explicitly feels me as it clarifies usage more, although
this part is up to you, I mean usage like:
fs->tx_packets += common_fwd_stream_transmit(fs, pkts, nb_pkts);