Subject: Re: [PATCH 3/3] chelsio: more rx speedup

From: Stephen Hemminger <[email-masked]>
Date: Tue, 9 Jan 2007 10:26:47 -0800

On Tue, 9 Jan 2007 09:42:03 +0100
Ingo Oeser <[email-masked]> wrote:

> Hi Stephen,
> 
> Stephen Hemminger schrieb:
> > --- netdev-2.6.orig/drivers/net/chelsio/sge.c
> > +++ netdev-2.6/drivers/net/chelsio/sge.c
> [...]
> > @@ -1043,45 +1046,42 @@ static void recycle_fl_buf(struct freelQ
> >   *	be copied but there is no memory for the copy.
> >   */
> >  static inline struct sk_buff *get_packet(struct pci_dev *pdev,
> > -					 struct freelQ *fl, unsigned int len,
> > -					 int dma_pad, int skb_pad,
> > -					 unsigned int copy_thres,
> > -					 unsigned int drop_thres)
> > +					 struct freelQ *fl, unsigned int len)
> >  {
> >  	struct sk_buff *skb;
> > -	struct freelQ_ce *ce = &fl->centries[fl->cidx];
> > +	const struct freelQ_ce *ce = &fl->centries[fl->cidx];
> >  
> > -	if (len < copy_thres) {
> > -		skb = alloc_skb(len + skb_pad, GFP_ATOMIC);
> > -		if (likely(skb != NULL)) {
> > -			skb_reserve(skb, skb_pad);
> > -			skb_put(skb, len);
> > -			pci_dma_sync_single_for_cpu(pdev,
> > -					    pci_unmap_addr(ce, dma_addr),
> > -					    pci_unmap_len(ce, dma_len),
> > -					    PCI_DMA_FROMDEVICE);
> > -			memcpy(skb->data, ce->skb->data + dma_pad, len);
> > -			pci_dma_sync_single_for_device(pdev,
> > +	if (len < copybreak) {
> > +		skb = alloc_skb(len + 2, GFP_ATOMIC);
> > +		if (!skb)
> > +			goto use_orig_buf;
> > +
> > +		skb_reserve(skb, 2);	/* align IP header */
> 
> Please use NET_IP_ALIGN here:

Wrong, NET_IP_ALIGN is intended to deal with platforms where alignment of DMA is more
important of alignment of structures.  Therefore if data is copied, it should
always be 2.

> 
> +		skb = alloc_skb(len + NET_IP_ALIGN, GFP_ATOMIC);
> +		if (!skb)
> +			goto use_orig_buf;
> +
> +		skb_reserve(skb, NET_IP_ALIGN);
> 
> > +		skb_put(skb, len);
> > +		pci_dma_sync_single_for_cpu(pdev,
> >  					    pci_unmap_addr(ce, dma_addr),
> >  					    pci_unmap_len(ce, dma_len),
> >  					    PCI_DMA_FROMDEVICE);
> > -		} else if (!drop_thres)
> > -			goto use_orig_buf;
> > -
> > +		memcpy(skb->data, ce->skb->data, len);
> > +		pci_dma_sync_single_for_device(pdev,
> > +					       pci_unmap_addr(ce, dma_addr),
> > +					       pci_unmap_len(ce, dma_len),
> > +					       PCI_DMA_FROMDEVICE);
> >  		recycle_fl_buf(fl, fl->cidx);
> >  		return skb;
> >  	}
> >  
> > -	if (fl->credits < drop_thres) {
> > +use_orig_buf:
> > +	if (fl->credits < 2) {
> 
> Why 2? What does this magic number mean?

No idea, it was there in the original. (as a parameter).

-- 
Stephen Hemminger <[email-masked]>