[ovs-dev] [PATCH 4/4] ovs: Implement 802.1ag Connectivity Fault Management

Ben Pfaff blp at nicira.com
Mon Nov 29 17:47:29 UTC 2010


On Sat, Nov 27, 2010 at 07:10:48PM -0800, Ethan Jackson wrote:
> Thanks for all the good feedback!  I should have paid a bit more
> attention to detail in the last version of the patch so sorry about
> that.  Hopefully what I just sent out will be better.
> 
> > In compose_and_send_ccm(), I would ofpbuf_reserve() two bytes before
> > putting in the Ethernet header to ensure proper alignment for data in
> > the ccm structure.
> 
> I don't quite follow this comment.  Why does this matter?  Is it still
> relevant in the revised patch I just sent out?

On x86, it's just a performance improvement: two bytes of padding plus
14 bytes of Ethernet header mean that 32- and 64-bit values are properly
aligned in what followed.

On RISC CPUs, it is a correctness problem, because misaligned accessed
cause bus errors (segfaults?  can't remember).




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