From: "Michael S. Tsirkin" <[EMAIL PROTECTED]> Date: Wed, 11 Oct 2006 02:13:38 +0200
> 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 :). You can't, it's a quality of implementation issue. We sendfile() pages directly out of the filesystem page cache without any blocking of modifications to the page contents, and the only way that works is if the card computes the checksum for us. If we sendfile() a page directly, we must compute a correct checksum no matter what the contents. We can't do this on the cpu before the data hits the device because another thread of execution can go in and modify the page contents which would invalidate the checksum and thus invalidating the packet. We cannot allow this. Blocking modifications is too expensive, so that's not an option either. - 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
