On Mon, 9 Oct 2006 19:47:05 +0200 "Michael S. Tsirkin" <[EMAIL PROTECTED]> wrote:
> Hi! > I'm trying to build a network device driver supporting a very large MTU > (around 64K) > on top of an infiniband connection, and I've hit a couple of issues I'd > appreciate some feedback on: > > 1. On the send side, > I've set NETIF_F_SG, but hardware does not support checksum offloading, > and I see "dropping NETIF_F_SG since no checksum feature" warning, > and I seem to be getting large packets all in one chunk. > The reason I've set NETIF_F_SG, is because I'm concerned that under real > life > stress Linux won't be able to allocate 64K of continuous memory. > > Is this concern of mine valid? I saw in-tree drivers allocating at least > 8K. > What's the best way to enable S/G on send side? > Is checksum offloading really required for S/G? Yes, in the current implementation, Linux needs checksum offload. But there is no reason, your driver can't compute the checksum in software. > 2. On the receive side, what's the best/right way to create an skb that > is larger than PAGE_SIZE? > Do I allocate with alloc_page and fill in nr_frags with skb_fill_page_desc? > Some drivers seem to fill in frag_list - which is better? > I see than even skb_put only works properly on linear skb. Allocating large buffers is problematic on busy systems. See lastest e1000 or sky2 that use frag_list. > What are the helpers legal for fragmented skb? Read the source. Setting up fragmented buffers has less helper functions, but isn't that hard. -- Stephen Hemminger <[EMAIL PROTECTED]> - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
