Re: [dpdk-stable] [PATCH] app/testpmd: fix random number of Tx segments

["Li, Xiaoyun" <xiaoyun.li@intel.com>]

Hi

> -----Original Message-----
> From: Zhang, AlvinX <alvinx.zhang@intel.com>
> Sent: Thursday, September 2, 2021 16:20
> To: Li, Xiaoyun <xiaoyun.li@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>
> Cc: dev@dpdk.org; Zhang, AlvinX <alvinx.zhang@intel.com>; stable@dpdk.org
> Subject: [PATCH] app/testpmd: fix random number of Tx segments
> 
> When random number of segments in Tx packets is enabled, the total data space
> length of all segments must be greater or equal than the size of an
> Eth/IP/UDP/timestamp packet, that's total 14 + 20 + 8 + 16 bytes. Otherwise the
> Tx engine may cause the application to crash.
> 
> Bugzilla ID: 797
> Fixes: 79bec05b32b7 ("app/testpmd: add ability to split outgoing packets")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Alvin Zhang <alvinx.zhang@intel.com>
> ---
>  app/test-pmd/config.c  | 16 +++++++++++-----  app/test-pmd/testpmd.c |  5
> +++++  app/test-pmd/testpmd.h |  5 +++++  app/test-pmd/txonly.c  |  7 +++++--
>  4 files changed, 26 insertions(+), 7 deletions(-)
> 
> diff --git a/app/test-pmd/config.c b/app/test-pmd/config.c index
> 31d8ba1..5105b3b 100644
> --- a/app/test-pmd/config.c
> +++ b/app/test-pmd/config.c
> @@ -3837,10 +3837,11 @@ struct igb_ring_desc_16_bytes {
>  	 * Check that each segment length is greater or equal than
>  	 * the mbuf data size.
>  	 * Check also that the total packet length is greater or equal than the
> -	 * size of an empty UDP/IP packet (sizeof(struct rte_ether_hdr) +
> -	 * 20 + 8).
> +	 * size of an Eth/IP/UDP + timestamp packet
> +	 * (sizeof(struct rte_ether_hdr) + 20 + 8 + 16).

I don't really agree on this. Most of the time, txonly generate packets with Eth/IP/UDP. It's not fair to limit the hdr length to include timestamp in all cases.
And to be honest, I don't see why you need to add "tx_pkt_nb_min_segs". It's only used in txonly when "TX_PKT_SPLIT_RND". So this issue is because when "TX_PKT_SPLIT_RND", the random nb_segs is not enough for the hdr.

But if you read txonly carefully, if "TX_PKT_SPLIT_RND", the first segment length should be equal or greater than 42 (14+20+8). Because when "TX_PKT_SPLIT_RND", update_pkt_header() should be called. And that function doesn't deal with header in multi-segments.
I think there's bug here.

So I think you should only add a check in pkt_burst_prepare() in txonly().
	if (unlikely(tx_pkt_split == TX_PKT_SPLIT_RND) || txonly_multi_flow)
+                           if (tx_pkt_seg_lengths[0] < 42) {
+			err_log;
+			return false;
+		}
		update_pkt_header(pkt, pkt_len);

As for timestamp, maybe refer to "pkt_copy_split" in csumonly.c is better? Copy the extra to the last segment if it's not enough. Not sure how to deal with this issue better.

>  	 */
>  	tx_pkt_len = 0;
> +	tx_pkt_nb_min_segs = 0;
>  	for (i = 0; i < nb_segs; i++) {
>  		if (seg_lengths[i] > mbuf_data_size[0]) {
>  			fprintf(stderr,
> @@ -3849,11 +3850,16 @@ struct igb_ring_desc_16_bytes {
>  			return;
>  		}
>  		tx_pkt_len = (uint16_t)(tx_pkt_len + seg_lengths[i]);
> +
> +		if (!tx_pkt_nb_min_segs &&
> +		    tx_pkt_len >= (sizeof(struct rte_ether_hdr) + 20 + 8 + 16))
> +			tx_pkt_nb_min_segs = i + 1;
>  	}
> -	if (tx_pkt_len < (sizeof(struct rte_ether_hdr) + 20 + 8)) {
> +
> +	if (!tx_pkt_nb_min_segs) {
>  		fprintf(stderr, "total packet length=%u < %d - give up\n",
> -				(unsigned) tx_pkt_len,
> -				(int)(sizeof(struct rte_ether_hdr) + 20 + 8));
> +			(unsigned int) tx_pkt_len,
> +			(int)(sizeof(struct rte_ether_hdr) + 20 + 8 + 16));
>  		return;
>  	}
> 
> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c index
> 6cbe9ba..c496e59 100644
> --- a/app/test-pmd/testpmd.c
> +++ b/app/test-pmd/testpmd.c
> @@ -232,6 +232,11 @@ struct fwd_engine * fwd_engines[] = {  };  uint8_t
> tx_pkt_nb_segs = 1; /**< Number of segments in TXONLY packets */
> 
> +/**< Minimum number of segments in TXONLY packets to accommodate all
> +packet
> + * headers.
> + */
> +uint8_t  tx_pkt_nb_min_segs = 1;
> +
>  enum tx_pkt_split tx_pkt_split = TX_PKT_SPLIT_OFF;  /**< Split policy for
> packets to TX. */
> 
> diff --git a/app/test-pmd/testpmd.h b/app/test-pmd/testpmd.h index
> 16a3598..f5bc427 100644
> --- a/app/test-pmd/testpmd.h
> +++ b/app/test-pmd/testpmd.h
> @@ -464,6 +464,11 @@ enum dcb_mode_enable  extern uint16_t
> tx_pkt_length; /**< Length of TXONLY packet */  extern uint16_t
> tx_pkt_seg_lengths[RTE_MAX_SEGS_PER_PKT]; /**< Seg. lengths */  extern
> uint8_t  tx_pkt_nb_segs; /**< Number of segments in TX packets */
> +
> +/**< Minimum number of segments in TXONLY packets to accommodate all
> +packet
> + * headers.
> + */
> +extern uint8_t  tx_pkt_nb_min_segs;
>  extern uint32_t tx_pkt_times_intra;
>  extern uint32_t tx_pkt_times_inter;
> 
> diff --git a/app/test-pmd/txonly.c b/app/test-pmd/txonly.c index
> aed820f..27e4458 100644
> --- a/app/test-pmd/txonly.c
> +++ b/app/test-pmd/txonly.c
> @@ -195,8 +195,11 @@
>  	uint32_t nb_segs, pkt_len;
>  	uint8_t i;
> 
> -	if (unlikely(tx_pkt_split == TX_PKT_SPLIT_RND))
> -		nb_segs = rte_rand() % tx_pkt_nb_segs + 1;
> +	if (unlikely(tx_pkt_split == TX_PKT_SPLIT_RND) &&
> +	    tx_pkt_nb_segs > tx_pkt_nb_min_segs)
> +		nb_segs = rte_rand() %
> +			  (tx_pkt_nb_segs - tx_pkt_nb_min_segs + 1) +
> +			  tx_pkt_nb_min_segs;
>  	else
>  		nb_segs = tx_pkt_nb_segs;
> 
> --
> 1.8.3.1