On 3/26/14, 2:16 AM, Ben Pfaff wrote:
On Mon, Mar 24, 2014 at 10:59:06AM -0700, Jarno Rajahalme wrote:
This patch shrinks the struct ofpbuf from 104 to 48 bytes on 64-bit
systems, or from 52 to 36 bytes on 32-bit systems (counting in the
'l7' removal by the previous patch). This may help contribute to
cache efficiency, and will speed up initializing, copying and
manipulating ofpbufs. This is potentially important for the DPDK
datapath, but the rest of the code base may also see a little benefit.
Changes are:
- Remove 'l7' pointer (previous patch).
- Use offsets instead of layer pointers for l2_5, l3, and l4 using
'l2' as basis. Usually 'data' is the same as 'l2', but this is not
always the case (e.g., when parsing or constructing a packet), so it
can not be easily used as the offset basis. Also, packet parsing is
faster if we do not need to maintain the offsets each time we pull
data from the ofpbuf.
- Use uint32_t for 'allocated' and 'size', as 2^32 is enough even for
largest possible messages/packets.
- Use packed enum for 'source'.
- Rearrange to avoid unnecessary padding.
- Remove 'private_p', which was used only in two cases, both of which
had the invariant ('l2' == 'data'), so we can temporarily use 'l2'
as a private pointer.
Signed-off-by: Jarno Rajahalme <jrajaha...@nicira.com>
Unfotunately I missed this patch until rebasing my layer 3 patch series
[1] today.
Before this patch, I set the 'l2' pointer to NULL and 'l3' to the start
of the network header to represent a layer 3 packet in a struct ofpbuf.
The way struct ofpbuf looks after this patch makes the assumption of
always having layer 2 headers a lot stronger.
I see two options for my patches going forward:
1) Add back 'l3' and remove 'l3_ofs' from struct ofpbuf (keeping the
rest as is); or
2) Encode a layer 3 packet by setting 'l2' to the network header address
and set l3_ofs to 0.
IMHO option 2 is not elegant, so I would prefer to avoid it. Are you OK
with option 1? Is there a better way I didn't think about?
-Lori
[1] https://github.com/ljakab/openvswitch/tree/l3_v3
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