Quoting r. Stephen Hemminger <[EMAIL PROTECTED]>: > > > > 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. > > > > > I'm worried whether an extra pass over data won't eat up all of > > the performance gains I get from the large MTU ... > > Yup, the cost is in touching the data, not in the copy.
Maybe I can patch linux to allow SG without checksum? Dave, maybe you could drop a hint or two on whether this is worthwhile and what are the issues that need addressing to make this work? I imagine it's not just the matter of changing net/core/dev.c :). -- MST - 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
