Re: [lwip-users] LWIP/WIN32 UDP performance (throughtput)

[Simon Goldschmidt]

Mason <address@hidden> wrote:
> > These are not used if you init autoip and dhcp correctly
> > (dhcp_set_struct(), autoip_set_struct()). I know that's not a good
> > solution and we should add pools for it.
> 
> This is all voodoo and black magic to me. It's very cool that you
> are so nice to explain stuff when questions are asked, but it
> really feels like there is a lot of high-level documentation
> missing, wouldn't you agree?

Of course I agree! It's just as always, writing the code is one thing, but 
writing documentation... :-)

> I think I'll err on the safe side, and make my port do the extra
> memcpy in the initial version. Then I can profile the different
> use-cases, and if there is a performance problem, then I'll see
> how to get rid of the copies. (Probably in 2-3 months)

That's probably the best idea.

> >> If no, that means I have to memcpy every outgoing frame, right?
> > 
> > Not if would redirect mem_malloc(). However, your platform would need
> > to allow the pbuf struct and payload be in contiguous memory, then.
> 
> I've been meaning to talk to you about this issue.
> Since I use DMA, there are hard constraints on the location of the buffer.
> It must start at an address multiple of 32 (cache line aligned) and the
> length must be a multiple of 32, and we must purge the appropriate lines
> from cache before the DMA operation.
> 
> I suppose I could allocate 32 more bytes to hold the pbuf struct and
> fudge the pointers to make the payload start on the right boundary,
> but you've said that pbuf_header could move the start of payload,
> or something like that... More voodoo stuff.

And that is something I need, too: using a different alignment constraint for 
pbufs (16 bytes) than for the rest (4 bytes). I might have to add that to 1.4.1 
so we can use a clean version in our products :-)

Simon
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