Re: [lwip-devel] UDP - transmission inefficiences

[Simon Goldschmidt]

Kieran Mansley wrote:
> It does highlight the problem of trying to optimise lwIP in this way
> though, as improvements for one platform can unintentionally hurt
> another.
> 
> Ideally inlining would be left up to the compiler as it should be in a
> good position to know when it would help and when it would not, but not
> all compilers are sophisticated enough to do this well.

Maybe the name Bill gave its patch is a bit misleading: it does not inline a 
function call but calculates the checksum when IP header bytes are saved. No 
compiler can do this on its own :-)

Of course this is architecture dependent: architectures with a big register 
file will be able to do the calculation in registers - they will gain from the 
patch. While architectures with a small register file will need many small 
memory accesses (even if it's only the cache which is accessed), which will 
slow them down.

Anyway, Bill's patch should be an option which is turned off by default. If so, 
I think it's worth including it.

Simon
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