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

[Mason]

Simon Goldschmidt wrote:

> Still, I think lwIP should be able to achieve the performance you want if:
> A) your netif driver correctly supports zero copy

A few months ago(*) we discussed zero-copy for DMA drivers,
and you wrote:

> For the RX side, using a *custom* PBUF_REF would be the best solution. 
> That's a pbuf that has a 'freed' callback and references external 
> memory. However, that doesn't work, yet (though I planned to add support 
> for it as I can see it's one possible solution to implement DMA MAC 
> drivers). The problem here is that pbuf_header() can't grow such pbufs 
> (as it doesn't know the original length). This would have to be fixed by 
> changing the struct pbuf (if only for PBUF_REF pbufs).

Is this mode supported in the trunk?
If yes, do you plan to port it to 1.4.1?
If no, that means I have to memcpy every incoming frame, right?

> As to the TX side: normally, TX pbufs are allocated as PBUF_RAM, the 
> memory for that is taken from the heap by calling mem_malloc(). Now the 
> simple solution would be to just replace mem.c by your own code 
> allocating and freeing from your TX pool: with the correct settings, 
> mem_malloc() isn't used for anything else buf PBUF_RAM pbufs. The only 
> problem might be that you don't know in advance how big the memory 
> blocks are (and thus how big your TX buffer entries should be), but by 
> using TCP_OVERSIZE, you can just use the maximum ethernet frame size (if 
> you don't mind wasting some RAM for smaller packets).

But when I looked,

I don't think it's possible to use mem_malloc as a packet
buffer allocator, as there are other types of uses, e.g.

  dhcp = (struct dhcp *)mem_malloc(sizeof(struct dhcp));
  autoip = (struct autoip *)mem_malloc(sizeof(struct autoip));

What I'd like is to be able to "redirect" pbuf_alloc to use
my buffer allocator, but the pbuf struct and the payload buffer
would not be contiguous, which violates the implicit assumptions
of PBUF_RAM pbufs, IIUC.

Have things changed on that front?
If no, that means I have to memcpy every outgoing frame, right?


(*) Date: Thu, 06 Oct 2011 16:10:07 +0200
http://lists.gnu.org/archive/html/lwip-users/2011-10/msg00008.html

-- 
Regards.