Re: [dpdk-dev] [PATCH v2] mbuf: fix compile by removing struct from function

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

> -----Original Message-----
> From: Van Haaren, Harry
> Sent: Thursday, January 10, 2019 6:07 PM
> To: dev@dpdk.org
> Cc: Van Haaren, Harry <harry.van.haaren@intel.com>; Pattan, Reshma
> <reshma.pattan@intel.com>; Dumitrescu, Cristian
> <cristian.dumitrescu@intel.com>; thomas@monjalon.net;
> olivier.matz@6wind.com
> Subject: [PATCH v2] mbuf: fix compile by removing struct from function
> 
> Although C compilation works with the struct rte_mbuf_sched
> declared inside the struct rte_mbuf namespace, C++ fails to
> compile.
> 
> This fix removes the temporary struct rte_mbuf_sched, instead
> reading from the mbuf directly for each struct member. As the
> struct is now not used directly, the C++ compiler doesn't need
> to know about the struct, resolving the issue.
> 
> Fixes: 5d3f72100904 ("mbuf: implement generic format for sched field")
> 
> Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
> 
> ---
> 
> Cc: reshma.pattan@intel.com
> Cc: cristian.dumitrescu@intel.com
> Cc: thomas@monjalon.net
> Cc: olivier.matz@6wind.com
> 
> See mailing list for v1 discussion, perhaps this solution is more
> readable due to leaving sched struct in-line in the mbuf struct.
> ---
>  lib/librte_mbuf/rte_mbuf.h | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index bc562dc8a..1b260efd5 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -2344,11 +2344,9 @@ rte_mbuf_sched_get(const struct rte_mbuf *m,
> uint32_t *queue_id,
>  			uint8_t *traffic_class,
>  			uint8_t *color)
>  {
> -	struct rte_mbuf_sched sched = m->hash.sched;
> -
> -	*queue_id = sched.queue_id;
> -	*traffic_class = sched.traffic_class;
> -	*color = sched.color;
> +	*queue_id = m->hash.sched.queue_id;
> +	*traffic_class = m->hash.sched.traffic_class;
> +	*color = m->hash.sched.color;
>  }
> 
>  /**
> @@ -2395,11 +2393,9 @@ rte_mbuf_sched_set(struct rte_mbuf *m,
> uint32_t queue_id,
>  			uint8_t traffic_class,
>  			uint8_t color)
>  {
> -	m->hash.sched = (struct rte_mbuf_sched){
> -				.queue_id = queue_id,
> -				.traffic_class = traffic_class,
> -				.color = color,
> -			};
> +	m->hash.sched.queue_id = queue_id;
> +	m->hash.sched.traffic_class = traffic_class;
> +	m->hash.sched.color = color;
>  }
> 
>  #ifdef __cplusplus
> --
> 2.17.1

NAK.

I am fine with V1, but against this V2 due to the reasons previously discussed and agreed by Olivier [1] regarding performance. We should not sacrifice performance for the sake of cosmetics criteria that can met some other way.

In order to meet readability requirements from Olivier, I suggest we go back to V1 and we explicitly mention the size of the mbuf->sched field inslide the mbuf as 8 bytes:

struct rte_mbuf {
	...
	struct rte_mbuf_sched sched; /**< Hierarchical scheduler: 8 bytes */
	...
}

Olivier, is this a good compromise?

Regards,
Cristian

[1] https://mails.dpdk.org/archives/dev/2018-December/121806.html