[PATCH] netvsc: optimize stats counters performance

[Stephen Hemminger]

On Fri, 2 Aug 2024 19:28:26 +0200
Morten Brørup <mb at smartsharesystems.com> wrote:

> > >  	ea = rte_pktmbuf_mtod(m, const struct rte_ether_addr *);
> > > -	if (rte_is_multicast_ether_addr(ea)) {
> > > -		if (rte_is_broadcast_ether_addr(ea))
> > > -			stats->broadcast++;
> > > -		else
> > > -			stats->multicast++;
> > > -	}
> > > +	RTE_BUILD_BUG_ON(offsetof(struct hn_stats, broadcast) !=
> > > +			offsetof(struct hn_stats, multicast) +  
> > sizeof(uint64_t));  
> > > +	if (unlikely(rte_is_multicast_ether_addr(ea)))
> > > +		(&stats->multicast)[rte_is_broadcast_ether_addr(ea)]++;
> > >  }  
> > 
> > This makes the code a little harder to read.  
> 
> I agree it is somewhat convoluted.
> It's a tradeoff... I preferred performance at the cost of making the code somewhat harder to read.
> The RTE_BUILD_BUG_ON() also helps showing what is going on with the weird indexing.

Optimizing for multicast packets is not worth bothering.
Keep the original code it is simpler.