Re: [PATCH v2] examples/l3fwd: support setting the data size of mbuf

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 18 Oct 2024 10:42:53 +0800
Chaoyong He <chaoyong.he@corigine.com> wrote:

> From: Long Wu <long.wu@corigine.com>
> 
> The previous code used a macro as the data size for mbuf
> to create the mempool and users cannot modify the size.
> 
> Now modify the code to support setting the data size of
> mbuf by '--mbuf-size' parameter. If user does not add the
> parameter in start command line, the default size is still
> 'RTE_MBUF_DEFAULT_BUF_SIZE'.
> 
> Examples:
> dpdk-l3fwd -l 0-3 -- -p 0x03 --mbuf-size=4096
> 
> Signed-off-by: Long Wu <long.wu@corigine.com>
> Reviewed-by: Chaoyong He <chaoyong.he@corigine.com>
> Acked-by: Morten Brørup <mb@smartsharesystems.com>
> 
> ---
> v2:
> * Modify some logic following the advices of reviewer.
> * Add the 'Acked-by' tag.
> ---
>  doc/guides/sample_app_ug/l3_forward.rst |  2 ++
>  examples/l3fwd/main.c                   | 31 ++++++++++++++++++++++---
>  2 files changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/sample_app_ug/l3_forward.rst b/doc/guides/sample_app_ug/l3_forward.rst
> index 1cc2c1dd1d..5afbbb242b 100644
> --- a/doc/guides/sample_app_ug/l3_forward.rst
> +++ b/doc/guides/sample_app_ug/l3_forward.rst
> @@ -143,6 +143,8 @@ Where,
>  * ``--alg=<val>:`` optional, ACL classify method to use, one of:
>    ``scalar|sse|avx2|neon|altivec|avx512x16|avx512x32``
>  
> +* ``--mbuf-size=N:`` Optional, Set the data size of mbuf to N bytes.
> +
>  * ``-E:`` Optional, enable exact match,
>    legacy flag, please use ``--lookup=em`` instead.
>  
> diff --git a/examples/l3fwd/main.c b/examples/l3fwd/main.c
> index 01b763e5ba..ed5d0c2608 100644
> --- a/examples/l3fwd/main.c
> +++ b/examples/l3fwd/main.c
> @@ -140,6 +140,7 @@ uint32_t max_pkt_len;
>  #ifdef RTE_LIB_EVENTDEV
>  static struct rte_mempool *vector_pool[RTE_MAX_ETHPORTS];
>  #endif
> +static uint16_t mbuf_data_size = RTE_MBUF_DEFAULT_DATAROOM;
>  static struct rte_mempool *pktmbuf_pool[RTE_MAX_ETHPORTS][NB_SOCKETS];
>  static uint8_t lkp_per_socket[NB_SOCKETS];
>  
> @@ -448,7 +449,8 @@ print_usage(const char *prgname)
>  		"                    One is ACL entry at while line leads with character '%c',\n"
>  		"                    another is route entry at while line leads with character '%c'.\n"
>  		"  --rule_ipv6=FILE: Specify the ipv6 rules entries file.\n"
> -		"  --alg: ACL classify method to use, one of: %s.\n\n",
> +		"  --alg: ACL classify method to use, one of: %s.\n"
> +		"  --mbuf-size=N: Set the data size of mbuf to N bytes.\n\n",
>  		prgname, RX_DESC_DEFAULT, TX_DESC_DEFAULT,
>  		ACL_LEAD_CHAR, ROUTE_LEAD_CHAR, alg);
>  }
> @@ -667,6 +669,22 @@ parse_lookup(const char *optarg)
>  	return 0;
>  }
>  
> +static void
> +parse_mbuf_data_size(const char *optarg)
> +{
> +	char *end = NULL;
> +
> +	mbuf_data_size = strtoul(optarg, &end, 10);
> +	if ((optarg[0] == '\0') || (end == NULL) || (*end != '\0'))
> +		rte_exit(EXIT_FAILURE, "Invalid mbuf data size: %s\n", optarg);
> +
> +	if (mbuf_data_size < RTE_ETHER_MIN_LEN ||
> +			mbuf_data_size > 0xFFFF - RTE_PKTMBUF_HEADROOM)

For clarity replace 0xffff with UINT16_MAX (which is data_len)

> +		rte_exit(EXIT_FAILURE,
> +				"mbuf-size should be >= %u and <= %u\n",
> +				RTE_ETHER_MIN_LEN, 0xFFFF - RTE_PKTMBUF_HEADROOM);
> +}
> +

Not sure why this is needed? What is the problem with the original code?
Are you trying to force packets to be segmented?