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

[Olivier Matz <olivier.matz@6wind.com>]

Hi,

On Thu, Jan 10, 2019 at 06:40:06PM +0000, Dumitrescu, Cristian wrote:
> 
> 
> > -----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?

Looks good to me, yes.


Thanks