From: Wei Liu Date: Sun, 22 Sep 2013 18:03:44 +0000 (+0100) Subject: xen-netback: improve ring effeciency for guest RX X-Git-Tag: v3.13-rc1~105^2~269 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4f0581d25827d5e864bcf07b05d73d0d12a20a5c;p=pandora-kernel.git xen-netback: improve ring effeciency for guest RX There was a bug that netback routines netbk/xenvif_skb_count_slots and netbk/xenvif_gop_frag_copy disagreed with each other, which caused netback to push wrong number of responses to netfront, which caused netfront to eventually crash. The bug was fixed in 6e43fc04a ("xen-netback: count number required slots for an skb more carefully"). Commit 6e43fc04a focused on backport-ability. The drawback with the existing packing scheme is that the ring is not used effeciently, as stated in 6e43fc04a. skb->data like: | 1111|222222222222|3333 | is arranged as: |1111 |222222222222|3333 | If we can do this: |111122222222|22223333 | That would save one ring slot, which improves ring effeciency. This patch effectively reverts 6e43fc04a. That patch made count_slots agree with gop_frag_copy, while this patch goes the other way around -- make gop_frag_copy agree with count_slots. The end result is that they still agree with each other, and the ring is now arranged like: |111122222222|22223333 | The patch that improves packing was first posted by Xi Xong and Matt Wilson. I only rebase it on top of net-next and rewrite commit message, so I retain all their SoBs. For more infomation about the original bug please refer to email listed below and commit message of 6e43fc04a. Original patch: http://lists.xen.org/archives/html/xen-devel/2013-07/msg00760.html Signed-off-by: Xi Xiong Reviewed-by: Matt Wilson [ msw: minor code cleanups, rewrote commit message, adjusted code to count RX slots instead of meta structures ] Signed-off-by: Matt Wilson Cc: Annie Li Cc: Wei Liu Cc: Ian Campbell [ liuw: rebased on top of net-next tree, rewrote commit message, coding style cleanup. ] Signed-off-by: Wei Liu Cc: David Vrabel Acked-by: Ian Campbell Signed-off-by: David S. Miller --- Reading git-diff-tree failed