Re: [B.A.T.M.A.N.] [PATCH] 32bit sequence number and TTL for broadcasts

[Marek Lindner <lindner_marek@yahoo.de>]

On Monday 26 April 2010 04:48:13 Sven Eckelmann wrote:
> First thing: it doesn't compile here :( (UML), but I am quite unsure if
>  this is a UML problem like many other things or a bigger problem.... it
>  seems that it is uml specific as ATOMIC64_INIT and other thingss are
>  defined, but the implementation of specific functions are missing... but
>  this is not the first time such thing happens with uml. Maybe someone with
>  some time can check different openwrt builds.
> 
> For example other architecture seems to use the generic implementation of
>  it: * arm
>  * parisc
>  * powerpc
>  * sh

I think Sven got a point here. It seems that for atomic64_t to work one needs 
a CPU which supports 64Bit operations otherwise the linux kernel will use its 
generic implementation. Apparently it uses an array of 16 spinlocks to provide 
this functionality. I wonder whether this might be a lot of overhead for our 
needs. Furthermore the generic implementation was added recently (as far as I 
can tell 2.6.30 does not have it) which raises the question of backward 
compatibility.

Regards,
Marek