Shmulik Hen wrote: > On Sunday 14 September 2003 01:41 am, Nick Patavalis wrote: > > this assumption, but I have also heard that "zero-copy" networking > > was added to the kernel at some point. Zero-copy indicates that > > data come directly for user-space and, hence, they might be > > non-continuous. > > You may want to take a look at e100_main.c in one of the latest 2.4.x > kernels. There you should be able to see how to deal with > dev->features and the flags NETIF_F_SG for scatter-gather > capabilities and NETIF_F_*_CSUM for checksum offloading capabilities. > Zero-copy was added in 2.4.4, and is a combination of the above. Also, > take a look at skbuff.h for MAX_SKB_FRAGS and struct skb_shared_info > and their use in the kernel code. In case it wasn't clear, if you _don't_ set those NETIF_* flags, then your driver is always passed contiguous data. performance penalty. > If not then I have to copy the packet to a > known-to-be-continuous area (e.g. a kmalloc-allocated one); this > caries a certain performance penalty. Your driver doesn't need to do it. Just don't set NETIF_F_SG and the kernel will arrange the data contiguously. Yes there is _sometimes_ a performance penalty, which is why the more advanced cards have these capabilities feature. -- Jamie - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
