From: Stanislaw Gruszka > Sent: 30 July 2019 10:36 ... > > + len = pkt_stat.pkt_len + pkt_offset; > > + skb = dev_alloc_skb(len); > > + if (WARN_ONCE(!skb, "rx routine starvation\n")) > > goto next_rp; > > > > /* put the DMA data including rx_desc from phy to new skb */ > > - skb_put_data(new, skb->data, new_len); > > + skb_put_data(skb, rx_desc, len); > > Coping big packets it quite inefficient. What drivers usually do is > copy only for small packets and for big ones allocate new rx buf > (drop packet alloc if fail) and pas old buf to network stack via > skb_add_rx_frag(). See iwlmvm as example. If you have to do iommu setup/teardown then the breakeven point for (not) copying may be surprisingly large. You do need to do the measurements on a range of hardware. Coping is also likely to affect the L1 cache - unless you can copy quickly without polluting the cache. It is all 'swings and roundabouts'. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
