Re: Question about __alloc_skb() speedup

[Eric Dumazet <eric.dumazet@gmail.com>]

Le samedi 04 décembre 2010 à 15:47 +0100, Eric Dumazet a écrit :
> Le samedi 04 décembre 2010 à 22:18 +0800, Junchang Wang a écrit :
> 
> > I added the prefetchw() in pktgen as follows:
> > 
> > diff --git a/net/core/pktgen.c b/net/core/pktgen.c
> > index 2953b2a..512f1ae 100644
> > --- a/net/core/pktgen.c
> > +++ b/net/core/pktgen.c
> > @@ -2660,6 +2660,7 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
> >  		sprintf(pkt_dev->result, "No memory");
> >  		return NULL;
> >  	}
> > +	prefetchw(skb->data);
> >  
> >  	skb_reserve(skb, datalen);
> >  
> > This time, I can check it without rebooting the system. The performance 
> > gain is 4%-5%(stable). Does 4% worth submitting it to the kernel?
> 
> Yes I believe so, pktgen being very specific, but I have few questions :
> 
> Is it with SLUB or SLAB ?
> 
> How many buffers in TX ring on you nic (ethtool -g eth0) ?
> 
> What is the datalen value here ? (you prefetch, then advance skb->data)
> 
> 32 or 64bit kernel ?
> 
> How many pps do you get before and after patch ?
> 
> Thanks
> 

Also, dont forget to include the prefetchw() in fill_packet_ipv6() as
well when submitting your patch.